[#321] add description of work of pre-commit hooks in CONTRIBUTING.md

CONTRIBUTING.md

@@ -8,8 +8,14 @@
 6. Make changes
 7. Checkout Makefile or README.md for commands like `make check` `make lint` `make test`
 8. Run tests and linters (`make check`)
-10. Commit your changes (`git commit -am 'Added some feature'`)
-11. Push to the branch (`git push origin my-new-feature`)
-12. Create new Pull Request
-13. Check if Request passed GithubActions
-14. Wait, until PR is reviewed
+9. Commit your changes (`git commit -am 'Added some feature'`)
+*When you install a project, scripts for pre-commit hooks are added to the .git folder.
+When you make your first commit, you will see the environment setting for the hooks in the terminal.
+This is normal behavior and will only happen on your first commit. In general, you will see in the terminal
+the status of checks for pre-commit hooks. Some hooks will make edits automatically and clean files will be
+added to the commit. Some (e.g. flake8) will display errors in the terminal and abort the commit to fix
+them. In this case, fix the errors and try to commit again. You can read more about pre-commit hooks [here](https://pre-commit.com/).*
+10. Push to the branch (`git push origin my-new-feature`)
+11. Create new Pull Request
+12. Check if Request passed GithubActions
+13. Wait, until PR is reviewed