[wp-docs] Codex authorization

[Otto]

The Codex is now authenticating against the normal wordpress.org
usernames and passwords. Old codex username and password combinations
will now no longer work.

Note: I fully expect this to have a few issues. Please email me
directly about any problems you find. Put “CODEX” in your subject
line.

Note 2: If you previously had your codex username as something
different than your normal forum username and you want to preserve
your editing history and such, email me as well. I can rename your old
username and correct the issue. I’ll need to know what your username
on the codex used to be and what your new username from the
wordpress.org forums is.

Note 3: Yes, cookies aren’t working fully. This will be resolved when
the forum upgrades are complete across the Extend sections as well.

-Otto