pidgin/nest

Add documentation and announcements for the pidginchat xmpp service

Testing Done:
Ran locally and in a container.

Reviewed at https://reviews.imfreedom.org/r/564/
Alan Hoskins <alanhoskins@gmail.com>
Elliott Sales de Andrade <quantum.analyst@gmail.com>
Frederick F. Kautz IV <fkautz@alumni.cmu.edu>
Gary Kramlich <grim@reaperworld.com>
Harrison <harrisonhopkins@gmail.com>
Jason Allan <code@jasonderrythomas.com>
John Bailey <rekkanoryo@rekkanoryo.org>
Richard Laager <rlaager@wiktel.com>
Robert Vehse <robertvehse@fastmail.fm>
Sorvival <sorvival@tutanota.com>
Zero <programmingzero@gmail.com>