Add MkDocs configuration and documentation rules for TrackGo

- Created a new `mkdocs.yml` file to define the structure and navigation for technical documentation.
- Updated `doc-updater.md` to clarify the role of the documentation specialist and the split between technical and user documentation.
- Introduced new rules in `documentation.mdc` and `technical-docs.mdc` to guide the creation of documentation, emphasizing the separation of technical and user content.
- Added a `readme.md` in the `docs` directory to provide instructions for using MkDocs with Backstage.

mkdocs.yml

@@ -0,0 +1,8 @@
+site_name: 'Concourse CI'
+
+nav:
+  - Home: index.md
+  - Android APK Build: android-apk-build.md
+
+plugins:
+  - techdocs-core