Dev guide updated for github/easy instructions?

[Watson Ladd]

This morning I realized that Pari is lagging behind, so went ahead to
start contributing a version bump. Unfortunately i completely forgot
the song and dance to make Macports process the portfile I produced,
and then the documentation was very pre-github migration (assumes
individual port files vs checking out the repo).

Perhaps we should have a development guide update, and in the meantime
do i just update the sources to include my local checkout? I could
have sworn I've done this before, but just forgot how.

Sincerely,
Watson

-- 
Astra mortemque praestare gradatim