Add Mastodon URL.

readme.mkd

@@ -69,6 +69,7 @@ Note that Java ME 8 has a Java 7 virtual machine with specific limitations.
    * [Mailing List](https://sourceforge.net/p/squirreljme/mailman/)
    * [SourceForge Project](http://www.sourceforge.net/projects/squirreljme)
  * Front facing social media:
+   * [Mastodon](https://mastodon.social/@XerTheSquirrel)
    * [Twitter](https://twitter.com/MultiPhasicApps)
    * [YouTube](https://www.youtube.com/channel/UCbmC7qQjeXUEUyE5XfDX5RA)
  * Personal Accounts (If you wish to contact me this way)