WIP: AuthenticationMD5 protocol documentation clarification

This is my first patch, so I hope I've got the process right for submitting
patches.

I'm building a driver to talk version 3.0 of the protocol, and generally
I've found the documentation to be excellent. One are I had trouble with
was responding to the AuthenticationMD5Password challenge. After receiving
help on IRC, I've attached a patch to the protocol documentation attempting
to clarify what is expected by the backend, basically:

concat(
'md5',
hex_encode(
md5(
concat(
hex_encode(
md5(
concat(password, username)
)
),
salt
)
)
)
)

My technical writing skills were not up to wording that in plain english,
and it seems like the rest of the documentation for the protocol steers
clear of anything that looks like code. Is this policy in this area or is
the code-esque description ok?

No code is changed, only documentation, so I've left out the code-relevant
patch info fields

Patch info:

Project name: postgresql
Branch: master

Cyan