ci: add quality to contributing

CONTRIBUTING.md

@@ -4,31 +4,51 @@ Thank you for contributing.
 
 See [Development](https://github.com/nvim-tree/nvim-tree.lua/wiki/Development) for environment setup, tips and tools.
 
+# Quality
+
+The following quality checks are mandatory and are performed during CI:
+
 ## Styling and formatting
 
 Code is formatted using luacheck, and linted using stylua.
-You can install these with:
+You may install these via your package manager or with:
 
 ```bash
 luarocks install luacheck
 cargo install stylua
 ```
 
+Run:
+```sh
+stylua lua
+luacheck lua
+```
+
 You can setup the git hooks by running `scripts/setup-hooks.sh`.
 
-## Adding new actions
+## Check
+
+[luals](https://luals.github.io) check is run with:
+
+```sh
+scripts/luals-check.sh
+```
+
+Requires `lua-language-server` on your path.
+
+# Adding new actions
 
 To add a new action, add a file in `actions/name-of-the-action.lua`. You should export a `setup` function if some configuration is needed.
 Once you did, you should run the `scripts/update-help.sh`.
 
-## Documentation
+# Documentation
 
 When adding new options, you should declare the defaults in the main `nvim-tree.lua` file.
 Once you did, you should run the `scripts/update-help.sh`.
 
 Documentation for options should also be added to `nvim-tree-opts` in `doc/nvim-tree-lua.txt`
 
-## Pull Request
+# Pull Request
 
 Please reference any issues in the description e.g. "resolves #1234".