docs: move event docstrings to the emitting line of code

src/client/websocket/handlers/MESSAGE_REACTION_ADD.js

@@ -2,5 +2,11 @@ const { Events } = require('../../../util/Constants');
 
 module.exports = (client, packet) => {
   const { user, reaction } = client.actions.MessageReactionAdd.handle(packet.d);
+  /**
+   * Emitted whenever a reaction is added to a cached message.
+   * @event Client#messageReactionAdd
+   * @param {MessageReaction} messageReaction The reaction object
+   * @param {User} user The user that applied the guild or reaction emoji
+   */
   if (reaction) client.emit(Events.MESSAGE_REACTION_ADD, reaction, user);
 };