fix: add doc generation target to tox

Author: pthierry-ledger

docs/Makefile

@@ -4,6 +4,7 @@ env_list =
   unittests
   build
   lint
+  doc
 isolated_build = true
 
 [tox:.package]
@@ -50,6 +51,14 @@ commands =
     black --line-length 90 --check --diff .
 
 
+[testenv:doc]
+extras = doc
+allowlist_externals =
+    {toxinidir}/genproto.sh
+commands =
+    {toxinidir}/genproto.sh
+    sphinx-build -b html -d docs/_build/doctress docs docs/_build
+
 [testenv:flake8]
 commands=flake8 {posargs}