bug#12560: 24.2; newsticker group support undocumented

[Max (☭)]

The newsticker RSS reader support creating groups and assigning feeds
into groups. However no group file format nor functions to move/assign
feeds into group are documented.

Newsticker should supply example group file in the same way it supply
example rss feeds. In addition to functions for feed assign/move there
should be function to explicitly save group file otherwise this
information is lost upon emacs exit.