Make target for creating a virtualenv.

Makefile

@@ -10,3 +10,7 @@ payload.zip: clean requirements.txt $(src)
 .PHONY = clean
 clean:
 	-rm -r payload.zip payload
+
+.venv: requirements.txt
+	python3 -m venv .venv
+	.venv/bin/pip install -r requirements.txt