This patch contains some minor updates to docs/howto.md for simplicity
and readability.
In particular removing the "testing" qualifier from Debian, since the
guide can be used on Debian stable, and also removing a clarification in
a comment about a very old version of chasquid.
This patch adds a brief how-to guide for setting up an email server with
Debian, dovecot and chasquid.
It is incomplete, but has enough information that it's ok to include it.
