add flake8 info to readme

Author: Um9i

README.md

@@ -72,3 +72,17 @@ With coverage:
 ```sh
 $ python manage.py cov
 ```
+
+###
+
+Run flake8 on the app:
+
+```sh
+$ python manage.py flake
+```
+
+or 
+
+```
+$ flake8 .
+```