Add markdownlint from Linux 201

Though we're not going to immediately use markdownlint here yet... Just for writers' reference.

Author: taoky

.markdownlint.jsonc

@@ -0,0 +1,20 @@
+{
+  "MD007": { // Unordered list indentation
+    "indent": 4
+  },
+  "MD013": false, // Line length
+  "MD033": { // Inline HTML
+    "allowed_elements": [
+      "br", // Useful in tables
+      "figure", "figcaption",
+      "s", "del" // Python-Markdown parsing issue with CJK
+    ]
+  },
+  "MD046": false, // Use fenced code block style, too many false positives
+  "MD051": false, // Link fragments should be valid, false positives
+  "MD052": false, // Reference link should be defined and used, false positives with includes/man.md
+  "MD010": false, // Some command output contains hard tabs
+  "MD024": {  // Allow multiple headers with the same content, if they are not siblings
+    "siblings_only": true
+  }
+}