fixup! docs: Add make rule to prepare venv similar to RTD build env

docs/Makefile

@@ -13,23 +13,27 @@ BUILDDIR      = build
 
 # Put it first so that "make" without argument is like "make help".
 help:
-	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+	@source venv/bin/activate && \
+	$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+
 livehtml:
-	@$(SPHINXAUTOBUILD) --watch ../leapp "$(SOURCEDIR)" "$(BUILDDIR)/html" $(SPHINXOPTS) $(0)
+	@source venv/bin/activate && \
+	$(SPHINXAUTOBUILD) --watch ../leapp "$(SOURCEDIR)" "$(BUILDDIR)/html" $(SPHINXOPTS) $(0)
 
 # Prepare virtualenv similar to the environment used during build on Read The Docs and install required packages
 env:
-	PY_VER=$$(sed -n -e 's/^\s*python:\s"\(.*\)"/\1/p' ../.readthedocs.yaml); \
+	# ad. pip install -r doesn't really work with relative paths :), so keeping it in the project root
+	@PY_VER=$$(sed -n -e 's/^\s*python:\s"\(.*\)"/\1/p' ../.readthedocs.yaml); \
 	echo $$PY_VER; \
 	rm -fr ./venv; \
-	virtualenv venv --python=python$$PY_VER; \
-	source venv/bin/activate; \
-	# pip install -r doesn't really work with relative paths :), so keeping it in the project root
+	virtualenv venv --python=python$$PY_VER && \
+	source venv/bin/activate && \
 	pushd .. && pip install -r requirements-docs.txt; popd
 
 # Catch-all target: route all unknown targets to Sphinx using the new
 # "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
 %: Makefile
-	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+	@source venv/bin/activate && \
+	$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
 
 .PHONY: all help Makefile env