Initial version of sphinx documentation and...

- remove ubuntu 21.04 from CI (end of life)
- adjust matrix strategy for clang.yml
- Use lessons learned from RetroArcher on localize.yml, crowdin.yml, and locale.py
- Add end of life comments to Dockerfiles
- Adjust dependency order in Dockerfiles

docs/source/building/build.rst

@@ -0,0 +1,31 @@
+:github_url: https://github.com/SunshineStream/Sunshine/tree/nightly/docs/source/building/build.rst
+
+Build
+=====
+Sunshine binaries are built using `CMake <https://cmake.org/>`_. Cross compilation is not
+supported. That means the binaries must be built on the target operating system and architecture.
+
+Building Locally
+----------------
+
+Clone
+^^^^^
+Ensure `git <https://git-scm.com/>`_ is installed and run the following:
+
+   .. code-block:: bash
+
+      git clone https://github.com/sunshinestream/sunshine.git --recurse-submodules
+      cd sunshine && mkdir build && cd build
+
+Build
+^^^^^
+See the section specific to your OS.
+
+Remote Build
+------------
+It may be beneficial to build remotely in some cases. This will enable easier building on different operating systems.
+
+#. Fork the project
+#. Activate workflows
+#. Trigger the `CI` workflow manually
+#. Download the artifacts/binaries from the workflow run summary