Add flake rule to Makefile

Makefile

@@ -4,6 +4,7 @@ define USAGE=
 @echo -e
 @echo -e "Usage:"
 @echo -e "\tmake black [arg=--<arg>]                 -- black formatting"
+@echo -e "\tmake flake                               -- run flake8"
 @echo -e "\tmake celery                              -- start celery worker"
 @echo -e "\tmake serve                               -- start source server"
 @echo -e "\tmake serve_target                        -- start target server"
@@ -25,6 +26,11 @@ black:
 	black . -l 80 --skip-string-normalization --exclude ".git|.venv|.tox|build|env|src|docs|migrations|versioneer.py" $(arg)
 
 
+.PHONY: flake
+flake:
+	flake8 .
+
+
 .PHONY: celery
 celery:
 	celery -A config worker -l info --beat