This should've been my first commit, ideally.

Following the advice in `tutorials/committers-guide/conventions.html',
added myself to the developers list, and removed myself from
additional-contributors.

Also, added a newsflash item stating the above fact.

Didn't quite know what the numbers in
ports/astro/xearth/files/freebsd.committers.markers meant. So, left
that alone :-)