[Twisted-Python] Tips for dev environment

[Adi Roiban]

I have updated the Twisted Development page with a section describing
how to create a dev environment.

https://twistedmatrix.com/trac/wiki/TwistedDevelopment#Creatingyourworkenvironment

Feel free to update or remove it.

------

>From previous discussions the direction was that new persons
contributing to Twisted should already know how to build a dev/work
environment and we should not instruct them how or what to do.

With the addition of setup.py optional component I find it useful to
remind developers about the optional dev component... so I have
updated the wiki page.

I would go further and instruct developers not to use the
pyflakes/pylint versions provided by the OS as they might be old or
too new for twistedchecker :)

Cheers,
-- 
Adi Roiban