docs: add readme

Signed-off-by: Pat Losoponkul <[email protected]>

README.md

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+# Identus Keycloak Plugins
+
+![CI](https://github.com/hyperledger/identus-keycloak-plugins/actions/workflows/unit-tests.yml/badge.svg)
+
+## Overview
+
+This repository provides a Keycloak Plugin that extends Keycloak's functionality to handle Self-Sovereign Identity (SSI) tasks, including OpenID for verifiable credential issuance.
+The plugin is designed to integrate with the Identus cloud agent, enabling a comprehensive SSI ecosystem.
+
+## Available Plugins
+
+### `identus-keycloak-oid4vci`
+
+Extends Keycloak for integration with Identus cloud agent in [OID4VCI](https://openid.net/specs/openid-4-verifiable-credential-issuance-1_0.html) flow.
+
+#### Features
+
+- Authorization code flow
+  - _AuthorizationRequest_ supported parameters
+    - [`issuer_state`](https://openid.net/specs/openid-4-verifiable-credential-issuance-1_0.html#section-5.1.3-2.3)
+  - _TokenResponse_ supported parameters
+    - [`c_nonce`](https://openid.net/specs/openid-4-verifiable-credential-issuance-1_0.html#section-6.2-4.1)
+    - [`c_nonce_expires_in`](https://openid.net/specs/openid-4-verifiable-credential-issuance-1_0.html#section-6.2-4.2)
+- Pre-authorized-code flow
+  - Not yet supported
+
+## Getting started
+
+### Using published docker image
+
+TODO
+
+### Using published JAR
+
+TODO