docs: Add/normalize .toString() docs on all classes (#2042)

* docs: Add/normalize .toString() examples on all classes

* docs: Remove exclamation point on ClientApplication#toString example

* docs: Normalize .toString() descriptions on all classes

* Use "returns" instead of "concatenates"

src/structures/DMChannel.js

@@ -27,9 +27,12 @@ class DMChannel extends Channel {
   }
 
   /**
-   * When concatenated with a string, this automatically concatenates the recipient's mention instead of the
-   * DM channel object.
+   * When concatenated with a string, this automatically returns the recipient's mention instead of the
+   * DMChannel object.
    * @returns {string}
+   * @example
+   * // Logs: Hello from <@123456789012345678>!
+   * console.log(`Hello from ${channel}!`);
    */
   toString() {
     return this.recipient.toString();