Update docs to: Add mode development to docs sidebar

Author: github-actions[bot]

mkdocs.yml

@@ -33,6 +33,7 @@ nav:
  - Contributing Guide: contributing.md
  - Open In Godot (Build): build.md
  - Create Action Scripts: create_action_scripts.md
+ - Mode Development: mode_development.md
 
 theme:
  name: readthedocs