Update internals.md

docs/internals.md

@@ -24,3 +24,23 @@ The code is statically analyzed with [Psalm](https://psalm.dev/). To run static
 ```shell
 ./vendor/bin/psalm
 ```
+
+## Rector
+
+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
+
+Use [ComposerRequireChecker](https://github.com/maglnet/ComposerRequireChecker) to detect transitive
+[Composer](https://getcomposer.org/) dependencies.
+
+To run the checker, execute the following command:
+
+```shell
+./vendor/bin/composer-require-checker
+```