Update Markdown validations

.rules/yamllint.yml

@@ -0,0 +1,13 @@
+# https://yamllint.readthedocs.io/en/stable/configuration.html#default-configuration
+
+extends: default
+
+rules:
+  anchors:
+    forbid-undeclared-aliases: true
+    forbid-duplicated-anchors: true
+
+  # 255 chars should be enough, but don't fail if a line is longer
+  line-length:
+    max: 200
+    #level: warning