docs: Reorganize RTD table of contents.

docs/code-contribution-checklist.rst

@@ -1,24 +0,0 @@
-=======================
-Code contribution guide
-=======================
-
-Thanks for contributing to Zulip! We hope this guide helps make the
-process smooth sailing for you.
-
-The "Ways to Contribute" and "How to get involved" sections of
-:doc:`readme-symlink` are a good place to start! After that, check out
-the tips below.
-
-
-.. toctree::
-   :maxdepth: 2
-
-   code-style
-   markdown
-   testing
-   logging
-   mypy
-   settings
-   front-end-build-process
-   queuing
-   schema-migrations

docs/index.rst

@@ -23,19 +23,56 @@ This set of documents covers installation and contribution instructions.
 
 Contents:
 
+* :ref:`user-docs`
+* :ref:`tutorial-docs`
+* :ref:`code-docs`
+* :ref:`system-docs`
+
+.. _user-docs:
+
 .. toctree::
-   :maxdepth: 3
+   :maxdepth: 2
+   :caption: Overview
 
    readme-symlink
    architecture-overview
+   directory-structure
+   roadmap
+   changelog
+
+.. _tutorial-docs:
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Developer tutorials
+
    integration-guide
    new-feature-tutorial
-   code-contribution-checklist
-   directory-structure
+
+.. _code-docs:
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Code contribution guide
+
+   code-style
+   testing
+   mypy
+
+.. _system-docs:
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Subsystem documentation
+
+   settings
+   queuing
+   markdown
+   front-end-build-process
+   schema-migrations
    full-text-search
    translating
-   changelog
-   roadmap
+   logging
 
 Indices and tables
 ==================