Fix docs (#130)

Co-authored-by: Sergei Predvoditelev <[email protected]>

README.md

@@ -31,6 +31,8 @@ The package provides:
 
 ## Installation
 
+The package could be installed with [Composer](https://getcomposer.org):
+
 ```shell
 composer require yiisoft/strings
 ```
@@ -241,46 +243,12 @@ if ($regexp->matches('second')) {
 }
 ```
 
-## Testing
-
-### Unit testing
-
-The package is tested with [PHPUnit](https://phpunit.de/). To run tests:
-
-```shell
-./vendor/bin/phpunit
-```
-
-### Mutation testing
-
-The package tests are checked with [Infection](https://infection.github.io/) mutation framework with
-[Infection Static Analysis Plugin](https://github.com/Roave/infection-static-analysis-plugin). To run it:
-
-```shell
-./vendor/bin/roave-infection-static-analysis-plugin
-```
-
-### Static analysis
-
-The code is statically analyzed with [Psalm](https://psalm.dev/). To run static analysis:
-
-```shell
-./vendor/bin/psalm
-```
-
-### Code style
-
-Use [Rector](https://github.com/rectorphp/rector) to make codebase follow some specific rules or
-use either newest or any specific version of PHP:
-
-```shell
-./vendor/bin/rector
-```
+## Documentation
 
-### Dependencies
+- [Internals](docs/internals.md)
 
-Use [ComposerRequireChecker](https://github.com/maglnet/ComposerRequireChecker) to detect transitive
-[Composer](https://getcomposer.org/) dependencies.
+If you need help or have a question, the [Yii Forum](https://forum.yiiframework.com/c/yii-3-0/63) is a good place for that.
+You may also check out other [Yii Community Resources](https://www.yiiframework.com/community).
 
 ## License
 

UPGRADE.md

@@ -1,4 +1,4 @@
-# Upgrading Instructions
+# Yii Strings Upgrading Instructions
 
 These notes highlight changes that could break your application when you upgrade package from one version to another.
 

docs/internals.md

@@ -0,0 +1,44 @@
+# Internals
+
+## Unit testing
+
+The package is tested with [PHPUnit](https://phpunit.de/). To run tests:
+
+```shell
+./vendor/bin/phpunit
+```
+
+## Mutation testing
+
+The package tests are checked with [Infection](https://infection.github.io/) mutation framework with
+[Infection Static Analysis Plugin](https://github.com/Roave/infection-static-analysis-plugin). To run it:
+
+```shell
+./vendor/bin/roave-infection-static-analysis-plugin
+```
+
+## Static analysis
+
+The code is statically analyzed with [Psalm](https://psalm.dev/). To run static analysis:
+
+```shell
+./vendor/bin/psalm
+```
+
+## Code style
+
+Use [Rector](https://github.com/rectorphp/rector) to make codebase follow some specific rules or
+use either newest or any specific version of PHP:
+
+```shell
+./vendor/bin/rector
+```
+
+## Dependencies
+
+This package uses [composer-require-checker](https://github.com/maglnet/ComposerRequireChecker) to check if
+all dependencies are correctly defined in `composer.json`. To run the checker, execute the following command:
+
+```shell
+./vendor/bin/composer-require-checker
+```