feat(docs): emit/event docs (gnolang#2047)

<!-- please provide a detailed description of the changes made in this
pull request. -->

## Description

This PR adds docs for emit/event. It adds reference docs, and a section
in effective Gno. More practical examples will be added to Gno By
Example.

Closes: gnolang#2003 

<details><summary>Contributors' checklist...</summary>

- [ ] Added new tests, or not needed, or not feasible
- [ ] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [ ] Updated the official documentation or not needed
- [ ] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [ ] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

---------

Co-authored-by: Lee ByeongJun <[email protected]>

docs/concepts/effective-gno.md

@@ -413,6 +413,73 @@ actual logic. This way, `privateMethod` can only be called from within the
 realm, and it can use the caller's address for authentication or authorization
 checks.
 
+### Emit Gno events to make life off-chain easier
+
+Gno provides users the ability to log specific occurrences that happened in their 
+on-chain apps. An `event` log is stored in the ABCI results of each block, and
+these logs can be indexed, filtered, and searched by external services, allowing 
+them to monitor the behaviour of on-chain apps.
+
+It is good practice to emit events when any major action in your code is 
+triggered. For example, good times to emit an event is after a balance transfer,
+ownership change, profile created, etc. Alternatively, you can view event emission
+as a way to include data for monitoring purposes, given the indexable nature of 
+events.
+
+Events consist of a type and a slice of strings representing `key:value` pairs.
+They are emitted with the `Emit()` function, contained in the `std` package in 
+the Gno standard library:
+
+```go
+package events
+
+import (
+	"std"
+)
+
+var owner std.Address
+
+func init() {
+	owner = std.PrevRealm().Addr()
+}
+
+func ChangeOwner(newOwner std.Address) {
+	caller := std.PrevRealm().Addr()
+
+	if caller != owner {
+		panic("access denied")
+	}
+
+	owner = newOwner
+	std.Emit("OwnershipChange", "newOwner", newOwner.String())
+}
+
+```
+If `ChangeOwner()` was called in, for example, block #43, getting the `BlockResults`
+of block #43 will contain the following data:
+
+```json
+{
+  "Events": [
+    {
+      "@type": "/tm.gnoEvent",
+      "type": "OwnershipChange",
+      "pkg_path": "gno.",
+      "func": "ChangeOwner",
+      "attrs": [
+        {
+          "key": "newOwner",
+          "value": "g1zzqd6phlfx0a809vhmykg5c6m44ap9756s7cjj"
+        }
+      ]
+    }
+    // other events
+  ]
+}
+```
+
+Read more about events [here](./stdlibs/events.md).
+
 ### Contract-level access control
 
 In Gno, it's a good practice to design your contract as an application with its

docs/concepts/stdlibs/coin.md

@@ -30,7 +30,6 @@ The `Coins` slice can be included in a transaction made by a user addresses or a
 Coins in this set are then available for access by specific types of Bankers,
 which can manipulate them depending on access rights.
 
-[//]: # (TODO ADD LINK TO Effective GNO)
-Read more about coins in the [Effective Gno](https://docs.gno.land/concepts/effective-gno/#native-tokens) section. 
+Read more about coins in the [Effective Gno](../effective-gno.md#coins) section. 
 
 The Coin(s) API can be found in under the `std` package [reference](../../reference/stdlibs/std/coin.md).

docs/concepts/stdlibs/events.md

@@ -0,0 +1,57 @@
+---
+id: events
+---
+
+# Gno Events
+
+## Overview
+
+Events in Gno are a fundamental aspect of interacting with and monitoring
+on-chain applications. They serve as a bridge between the on-chain environment 
+and off-chain services, making it simpler for developers, analytics tools, and 
+monitoring services to track and respond to activities happening in Gno.land.
+
+Gno events are pieces of data that log specific activities or changes occurring 
+within the state of an on-chain app. These activities are user-defined; they might
+be token transfers, changes in ownership, updates in user profiles, and more.
+Each event is recorded in the ABCI results of each block, ensuring that action 
+that happened is verifiable and accessible to off-chain services. 
+
+## Emitting Events
+
+To emit an event, you can use the `Emit()` function from the `std` package 
+provided in the Gno standard library. The `Emit()` function takes in a string 
+representing the type of event, and an even number of arguments after representing
+`key:value` pairs. 
+
+Read more about events & `Emit()` in 
+[Effective Gno](../effective-gno.md#emit-gno-events-to-make-life-off-chain-easier),
+and the `Emit()` reference [here](../../reference/stdlibs/std/chain.md#emit).
+
+## Data contained in a Gno Event
+
+An event contained in an ABCI response of a block will include the following
+data:
+
+``` json
+{
+    "@type": "/tm.gnoEvent", // TM2 type
+    "type": "OwnershipChange", // Type/name of event defined in Gno
+    "pkg_path": "gno.land/r/demo/example", // Path of the emitter
+    "func": "ChangeOwner", // Gno function that emitted the event
+    "attrs": [ // Slice of key:value pairs emitted
+        {
+            "key": "oldOwner",
+            "value": "g1jg8mtutu9khhfwc4nxmuhcpftf0pajdhfvsqf5"
+        },
+        {
+            "key": "newOwner",
+            "value": "g1zzqd6phlfx0a809vhmykg5c6m44ap9756s7cjj"
+        }
+    ]
+}
+```
+
+You can fetch the ABCI response of a specific block by using the `/block_results` 
+RPC endpoint.
+

docs/reference/stdlibs/std/chain.md

@@ -28,6 +28,19 @@ std.AssertOriginCall()
 ```
 ---
 
+## Emit
+```go
+func Emit(typ string, attrs ...string)
+```
+Emits a Gno event. Takes in a **string** type (event identifier), and an even number of string 
+arguments acting as key-value pairs to be included in the emitted event.
+
+#### Usage
+```go
+std.Emit("MyEvent", "myKey1", "myValue1", "myKey2", "myValue2")
+```
+---
+
 ## CurrentRealmPath
 ```go
 func CurrentRealmPath() string
@@ -117,7 +130,8 @@ currentRealm := std.CurrentRealm()
 ```go
 func PrevRealm() Realm
 ```
-Returns the previous caller realm (can be realm or EOA). If caller is am EOA, `pkgpath` will be empty.
+Returns the previous caller realm (can be code or user realm). If caller is a
+user realm, `pkgpath` will be empty.
 
 #### Usage
 ```go