... as it seems to hard for some people

Added a little generic info section about the lists and a section about
how to deal with trolls and spam on the lists.

This is a new documentation for the source tree. This information has
been present since a long time at
http://curl.haxx.se/mail/etiquette.html but now it is put into a plain
text version too for wider distribution. The web version will be
automatically generated from this source document.