[9fans] remedial sources auth, connect, and mount in plan9port

[Jason Catena <jason.catena@gmail.com>]

Geoff was kind enough to provide to me a contrib directory on sources,
so I'm now trying to write into it.

I can't seem to get the hang of the authorization, connection, and
mount steps necessary for an authorized mount of sources in plan9port,
so I can just copy files into my contrib directory.  Over several
dozen attempts to understand factotum, it never saves any actual data
for me, so I apparently have some serious misunderstandings.

For the mount, I can use the following to mount sources read-only, but
I can't save anything into it.
sudo 9mount 'tcp!sources.cs.bell-labs.com' /n/sources

9fs sources also doesn't seem to provide an authenticated connection,
or a mount.

Would someone be kind enough to chant the few magic plan9(port)
incantations with which I can store my sources-server username and
password with factotum, connect to sources, and mount sources
(specifically, my directory) as a writable filesystem?   I promise
diligent study, to understand what the commands do.

Jason Catena