Bug 1967634 - Add python-sites lint to facilitate adding rules specific to python/sites/ r=ahal

Differential Revision: https://phabricator.services.mozilla.com/D250374

docs/code-quality/lint/linters/python-sites.rst

@@ -0,0 +1,40 @@
+Python Sites
+==================
+
+This linter verifies that :searchfox:`python site <python/sites/>` files are
+following the best practices.
+
+Redundant Specifications
+--------------------------------
+
+If a dependency is specified in the :searchfox:`mach site <python/sites/>`, it
+does not need to be specified in any command site (eg: `build.txt`, `common.txt`, etc).
+
+This check warns against these redundant specifications, and can also fix them.
+
+Specification Ordering
+--------------------------------
+
+The first line of any site file should start with `require-python:`. All subsequent lines
+should be sorted alphabetically. This check ensures that's the case, and can fix the ordering
+for you, while still maintaining comment block association.
+
+Run Locally
+-----------
+
+This mozlint linter can be run using mach:
+
+.. parsed-literal::
+
+    $ mach lint --linter python-sites <file paths>
+
+Configuration
+-------------
+
+This linter is enabled by default, and will run if you make changes to site files.
+
+Sources
+-------
+
+* :searchfox:`Configuration (YAML) <tools/lint/python-sites.yml>`
+* :searchfox:`Source <tools/lint/python-sites/__init__.py>`