Add rule to tox.ini to build sphinx docs

tox.ini

@@ -86,6 +86,23 @@ commands =
     -coverage combine --append
     coverage xml --include="./src/*" --omit="*/admin.py,*/test*,*/migrations/*"
 
+[testenv:docs]
+description = Build the Sphinx documentation
+deps =
+    -r requirements/dev.txt
+    -r requirements-django42.txt
+
+package = editable
+setenv =
+    PYTHONPATH = {toxinidir}/python:{toxinidir}/tests
+    DJANGO_SETTINGS_MODULE = argus.site.settings.dev
+    LC_ALL=C.UTF-8
+    LANG=C.UTF-8
+    VIRTUALENV_PIP=23.1.0
+commands_pre =
+commands =
+    sphinx-build -M html docs/ docs/_build/
+
 [testenv]
 passenv = DATABASE_URL