Add docs on how to configure Pycharm for GDScript

**Your Godot version:** Latest

**Issue description:** It would be nice to enhance the docs for GDScript and Pycharm as an external Editor. There already is a description for Rider but I think this is more related to the Mono version with C#.

**URL to the documentation page (if already existing):**

- ( Repository link ) https://github.com/godotengine/godot-docs/blob/master/tutorials/editor/external_editor.rst
- ( Official docs link ) https://docs.godotengine.org/en/stable/tutorials/editor/external_editor.html