Source venv to install packages in it

Encountered while setting up the "venv-debian", looks like we need it on
the other setup as well. Works well for me locally.

Makefile

@@ -4,14 +4,19 @@ all: help
 .PHONY: venv-debian
 venv-debian: ## Provision a Python 3 virtualenv for development on a prod-like system that has installed dependencies specified in https://github.com/freedomofpress/securedrop-debian-packaging/blob/main/securedrop-client/debian/control
 	python3 -m venv .venv-debian --system-site-packages
-	.venv-debian/bin/pip install --upgrade pip wheel
-	.venv-debian/bin/pip install --require-hashes -r "requirements/dev-requirements-debian.txt"
+	. .venv-debian/bin/activate && .venv-debian/bin/pip install --upgrade pip wheel
+	. .venv-debian/bin/activate && .venv-debian/bin/pip install --require-hashes -r "requirements/dev-requirements-debian.txt"
+	@echo "#################"
+	@echo "Virtualenv with Debian system-packages is complete."
+	@echo "Make sure to install the apt packages for system Qt."
+	@echo "Then run: source .venv-debian/bin/activate"
+
 
 .PHONY: venv
 venv: ## Provision a Python 3 virtualenv for development
 	python3 -m venv .venv
-	.venv/bin/pip install --upgrade pip wheel
-	.venv/bin/pip install --require-hashes -r "requirements/dev-requirements.txt"
+	. .venv/bin/activate && .venv/bin/pip install --upgrade pip wheel
+	. .venv/bin/activate && .venv/bin/pip install --require-hashes -r "requirements/dev-requirements.txt"
 
 SEMGREP_FLAGS := --exclude "tests/" --error --strict --verbose