Adding code of conduct and Markdownlint

.pre-commit-config.yaml

@@ -39,3 +39,12 @@ repos:
         args:
           - --line-length=120
           - --profile=black
+
+-   repo: https://github.com/igorshubovych/markdownlint-cli
+    rev: v0.30.0
+    hooks:
+    -   id: markdownlint
+        args:
+          [
+            "--disable=MD041"
+          ]