Add comprehensive documentation for Quizzical Beats

- Created a detailed database schema document outlining tables, relationships, and key fields.
- Added OAuth integration documentation covering Spotify and Dropbox authentication processes.
- Introduced a FAQ section addressing common user inquiries about the application.
- Developed a user-friendly index page for easy navigation of the documentation.
- Specified documentation dependencies in requirements.txt for building the documentation site.
- Expanded user guide with sections on account management, creating rounds, exporting rounds, getting started, importing songs, and user interface navigation.
- Updated mkdocs.yml for improved site structure and navigation.

docs/requirements.txt

@@ -0,0 +1,7 @@
+# Documentation dependencies
+mkdocs>=1.4.0
+mkdocs-material>=9.0.0
+mkdocstrings>=0.21.0
+mkdocstrings-python>=1.0.0
+pymdown-extensions>=9.0
+Pygments>=2.14.0