Document how dependency changes should be made (#2)

* Add basic doc on making dep changes based on previously written one

Author: Jackenmen

source/dependency-changes.rst

@@ -0,0 +1,19 @@
+Making dependency changes
+=========================
+
+Updating Python package dependencies
+------------------------------------
+
+To update all dependencies, the GitHub Actions workflow for generating requirements files should be used:
+https://github.com/Cog-Creators/Red-DiscordBot/actions/workflows/run_pip_compile.yaml
+
+Run the above workflow and, after it finishes, download the "merged" artifact archive.
+Copy all of the files from this archive to the ``requirements/`` directory in the repository,
+overriding any already present files. Now, you can look at the git diff to see
+which dependency versions changed.
+
+When updating a dependency to a newer version:
+
+- Verify that all code commented with ``DEP-WARN`` is not affected by the new dependency versions
+- Read the changelogs for dependencies to make sure there are no (breaking) changes
+  that may affect our code

source/index.rst

@@ -11,3 +11,4 @@ Full Table of Contents
    :maxdepth: 3
 
    core-devs/index
+   dependency-changes