[Docs] Add version guarantees (#2882)

Make some version guarantees.

We also need to do a pass over the existing things this would cover and decide if any of them should be made private.

changelog.d/2882.docs.rst

@@ -0,0 +1 @@
+Create documentation covering what we consider a developer facing breaking change and guarantees regarding them.

docs/guide_cog_creation.rst

@@ -35,6 +35,20 @@ a text editor or IDE (examples include `Sublime Text 3 <https://www.sublimetext.
 `Visual Studio Code <https://code.visualstudio.com/>`_, `Atom <https://atom.io/>`_, and
 `PyCharm <http://www.jetbrains.com/pycharm/>`_).
 
+.. attention:: 
+    While you can intentionally override Red's cogs/extensions, this may break things.
+    We would prefer if people wanted custom behavior
+    for any core cog/extension, an issue and/or PR is made
+    Overriding Permissions specifically is dangerous.
+
+    Subclassing to make changes to Red's cogs/extensions
+    may not be a safe way to stay up to date either,
+    as changes to cogs and their interactions with red
+    are not guaranteed to not be breaking.
+
+    Any cogs doing this are doing so at their own risk,
+    and should also inform users of associated risks.
+
 --------------
 Creating a cog
 --------------

docs/index.rst

@@ -43,6 +43,7 @@ Welcome to Red - Discord Bot's documentation!
     framework_modlog
     framework_rpc
     framework_utils
+    version_guarantees
 
 .. toctree::
     :maxdepth: 2

docs/version_guarantees.rst

@@ -0,0 +1,36 @@
+.. _version-guarantees:
+
+==========
+Versioning
+==========
+
+Red is versioned as ``major.minor.micro``
+
+While this is very similar to SemVer, we have our own set of guarantees.
+
+Major versions are for project wide rewrites and are not expected in the foreseeable future.
+
+==========
+Guarantees
+==========
+
+Anything in the ``redbot.core`` module or any of its submodules 
+which is not private (even if not documented) should not break without notice.
+
+Anything in the ``redbot.cogs`` module or any of it's submodules is specifically
+excluded from being guaranteed.
+
+If you would like something in here to be guaranteed,
+open an issue making a case for it to be moved.
+
+=======================
+Breaking Change Notices
+=======================
+
+Breaking changes in Red will be noted in the changelog with a special section.
+
+Breaking changes may only occur on a minor or major version bump.
+
+A change not covered by our guarantees may not be considered breaking for these purposes, 
+while still being documented as a breaking change in internal documentation
+for the purposes of other internal APIs.