docs(*): add links to Discord's API objects & data (#5862)

src/structures/MessageAttachment.js

@@ -9,7 +9,7 @@ class MessageAttachment {
   /**
    * @param {BufferResolvable|Stream} attachment The file
    * @param {string} [name=null] The name of the file, if any
-   * @param {Object} [data] Extra data
+   * @param {APIAttachment} [data] Extra data
    */
   constructor(attachment, name = null, data) {
     this.attachment = attachment;
@@ -102,3 +102,8 @@ class MessageAttachment {
 }
 
 module.exports = MessageAttachment;
+
+/**
+ * @external APIAttachment
+ * @see {@link https://discord.com/developers/docs/resources/channel#attachment-object}
+ */