chore: add markdownlint config to suppress Codacy false positives

Disable MD013 (line length) and MD025 (first heading level) — both are
false positives for Docusaurus projects.

Author: charlypa

.markdownlint.json

@@ -0,0 +1,4 @@
+{
+  "MD013": false,
+  "MD025": false
+}