Update README.md

Explain how to format and type check.

(cherry picked from commit f8217c9d)

README.md

@@ -94,6 +94,17 @@ Please run `alembic upgrade head` after pulling changes from the repository.
 
 ---
 
+## Compliance
+
+### Formatting
+
+We use [black](https://github.com/psf/black) as formatting tool.
+Use `black .` to run the formatter.
+
+### Static Type Checking
+
+Run `mypy .` to let [mypy](https://www.mypy-lang.org/) validate the Python types.
+
 ## How to move around in this repo
 
 ## `/portal/`: Main Application