chore(pre-commit): add markdownlint validation

Author: sebastien-boulle

.pre-commit-config.yaml

@@ -17,6 +17,12 @@ repos:
     rev: master  # or a specific git tag from md-toc
     hooks:
       - id: md-toc
+
+  - repo: git://github.com/igorshubovych/markdownlint-cli
+    rev: v0.23.2
+    hooks:
+      - id: markdownlint
+
   - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v2.0.0
     hooks:
@@ -31,4 +37,4 @@ repos:
       - id: detect-private-key
       - id: end-of-file-fixer
       - id: trailing-whitespace
-        exclude: (.github/CODEOWNERS|validator.bats)
+        exclude: (.github/CODEOWNERS)