Add MkDocs Click to doc contributing (#502)

docs/contributing/documentation.md

@@ -9,6 +9,7 @@ The project documentation website is based on [MkDocs framework](https://www.mkd
 - [Mkdocs Material](https://squidfunk.github.io/mkdocs-material/): theme and framework
 - [Mike](https://github.com/jimporter/mike): to publish multiple versions
 - [MkDocs Coverage](https://github.com/pawamoy/mkdocs-coverage): to integrate coverage report iframe into MkDocs
+- [MkDocs Click](https://github.com/mkdocs/mkdocs-click): generate documentation for Click command line applications
 - [MkDocs GitLab plugin](https://pypi.org/project/mkdocs-gitlab-plugin/): to display links to GitLab references items: used in the changelog page
 
 Please refer to their respective documentation.