Add pre-commit

.pre-commit-config.yaml

@@ -0,0 +1,13 @@
+repos:
+    - repo: https://github.com/ambv/black
+      rev: 19.3b0
+      hooks:
+        - id: black
+          language_version: python3
+
+    - repo: https://github.com/pre-commit/pre-commit-hooks
+      rev: v2.2.3
+      hooks:
+        - id: trailing-whitespace
+        - id: end-of-file-fixer
+        - id: flake8