add NodePath#addComment method

src/babel/traversal/path/removal.js

@@ -58,6 +58,20 @@ export function _assertUnremoved() {
   }
 }
 
+/**
+ * Description
+ */
+
+export function addComment(type, content) {
+  var node = this.node;
+  var key = `${type}Comments`;
+  var comments = node[key] = node[key] || [];
+  comments.push({
+    type: "CommentBlock",
+    value: content
+  });
+}
+
 /**
  * Share comments amongst siblings.
  */