build: add pre-commit hooks

Including black

Author: boriel

.pre-commit-config.yaml

@@ -0,0 +1,11 @@
+repos:
+  -   repo: https://github.com/pre-commit/pre-commit-hooks
+      rev: v2.3.0
+      hooks:
+        -   id: check-yaml
+        -   id: end-of-file-fixer
+        -   id: trailing-whitespace
+  -   repo: https://github.com/psf/black
+      rev: 19.3b0
+      hooks:
+        -   id: black