Fixed #36485 -- Added lint-docs check in Tox and GitHub Actions.

The `check` docs target now runs spelling, black, and lint, so all
current documentation quality checks can be run with a single command.

Also documented the lint-docs check's availability and usage.

docs/internals/contributing/writing-code/unit-tests.txt

@@ -69,11 +69,11 @@ command from any place in the Django source tree:
     $ tox
 
 By default, ``tox`` runs the test suite with the bundled test settings file for
-SQLite, ``black``, ``blacken-docs``, ``flake8``, ``isort``, and the
-documentation spelling checker. In addition to the system dependencies noted
-elsewhere in this documentation, the command ``python3`` must be on your path
-and linked to the appropriate version of Python. A list of default environments
-can be seen as follows:
+SQLite, ``black``, ``blacken-docs``, ``flake8``, ``isort``, ``lint-docs`` and
+the documentation spelling checker. In addition to the system dependencies
+noted elsewhere in this documentation, the command ``python3`` must be on your
+path and linked to the appropriate version of Python. A list of default
+environments can be seen as follows:
 
 .. console::
 
@@ -84,6 +84,7 @@ can be seen as follows:
     flake8>=3.7.0
     docs
     isort>=5.1.0
+    lint-docs
 
 Testing other Python versions and database backends
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

docs/internals/contributing/writing-documentation.txt

@@ -158,8 +158,9 @@ Documentation quality checks
 ----------------------------
 
 Several checks help maintain Django's documentation quality, including
-:ref:`spelling <documentation-spelling-check>` and
-:ref:`code block formatting <documentation-code-block-format-check>`.
+:ref:`spelling <documentation-spelling-check>`,
+:ref:`code block formatting <documentation-code-block-format-check>`, and
+:ref:`documentation style <documentation-lint-check>`.
 
 These checks are run automatically in CI and must pass before documentation
 changes can be merged. They can also be run locally with a single command:
@@ -215,6 +216,31 @@ installed, run the following command from the ``docs`` directory:
 The formatter will report any issues by printing them to the terminal and will
 reformat code blocks where possible.
 
+.. _documentation-lint-check:
+
+Documentation lint check
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Django's documentation is checked for reStructuredText style and formal issues
+using :pypi:`sphinx-lint`. This helps catch problems like stray tabs, trailing
+whitespace, excessive line length, and similar formatting problems.
+
+Once ``sphinx-lint`` is installed, the check can be run with the following
+command from the ``docs`` directory:
+
+.. console::
+
+     $ make lint
+
+The command prints any violations to the terminal in the form
+``path:line: message``. If problems are encountered:
+
+* Read the message and fix the indicated issue (for example, remove trailing
+  whitespace, adjust backticks, or replace tabs with spaces).
+* For long lines consider wrapping text onto new lines or breaking long inline
+  links into named references. The custom line length check should already skip
+  common false positives such as headings, tables and long links.
+
 .. _documentation-link-check:
 
 Link check