Adopt Black

README.md

@@ -94,3 +94,7 @@ Hosts", turn off "Host Sending Client Registration Request Must Match" and save
 it.
 
 Now run: `pytest --issuer=http://localhost:8080/auth/realms/master`
+
+### Code formatting
+
+We are using [Black](https://github.com/ambv/black) for code formatting.

docs/architecture/decisions/0013-black-code-formatter.md

+# 13. Black code formatter
+
+Date: 2018-06-12
+
+## Status
+
+Accepted
+
+## Context
+
+We would like to simplify code reviews and unify code style.
+
+## Decision
+
+Use Black code formatter: https://github.com/ambv/black
+
+## Consequences
+
+Less thinking about formatting and more about functionality.