Rebuild doc venv if requirements.txt changes
@@ -16,7 +16,7 @@ BUILDDIR = build
help: .venv
@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
-.venv:
+.venv: requirements.txt
@echo Creating Python venv for Sphinx build
python3 -m venv .venv
.venv/bin/pip -q install --upgrade pip
