Makefile: Add a make lint-python command

Fixes #45

Makefile

diff --git a/Makefile b/Makefile
index 4f37195..64e2a09 100644
--- a/Makefile
+++ b/Makefile
@@ -52,6 +52,11 @@
 
 .PHONY: check-licenses
 
+lint-python:
+	@python3 -m flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+
+.PHONY: lint-python
+
 
 check: check-licenses
 	@true