Add pre-commit

.pre-commit-config.yaml

@@ -0,0 +1,15 @@
+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
+-   repo: https://github.com/thlorenz/doctoc
+    rev: v1.4.0
+    hooks:
+    -   id: doctoc