build docs during tox

tox.ini

 [tox]
-envlist = lint, typecheck
+envlist = lint, typecheck, docs
 
 [testenv:lint]
 description = Lint code with Ruff
@@ -9,4 +9,16 @@ commands = ruff check mapping_provider
 [testenv:typecheck]
 description = Type-check code with mypy
 deps = mypy
-commands = mypy mapping_provider
\ No newline at end of file
+commands = mypy mapping_provider
+
+[testenv:docs]
+description = Build docs
+deps =
+    sphinx
+    sphinx-rtd-theme
+    sphinxcontrib-plantuml
+    sphinxcontrib-drawio
+    sphinxcontrib-openapi
+commands = sphinx-build -b html docs/source docs/build
+
+