chore: enforce markdownlint on *.md files

Author: brianrodri

.markdownlint.json

@@ -0,0 +1,4 @@
+{
+    "$schema": "https://raw.githubusercontent.com/DavidAnson/markdownlint/refs/heads/main/schema/markdownlint-config-schema.json",
+    "extends": "markdownlint/style/prettier"
+}