Write a page for new contributors

In conversation with @ceboudreaux in
[IRC](https://botbot.me/freenode/gittip/msg/4258008/) and @heidigardner
on #1120, it came out that Gittip has many sources of information and
it's hard to get oriented as a new contributor. Here's a page that aims
to fix this problem.
Learn to count
Rework first paragraph of /for/contributors/

Per feedback from @heidigardner and @ceboudreaux.

 - "new kind of company" -> "new kind of organization"
 - change "share" to "take" to indicate method of distribution
 - add two links and move a third
Specify that it's the *email* newsletter
Update balanced account links for new dashboard

Balanced has a new dashboard now, and we should use it (it has a
different URL).
Add departments and call to action
Up min threads for @jeresig
Bump version to 9.3.39
Bump version to 9.3.39-dev
Merge branch 'master' of github.com:gittip/www.gittip.com
Evasive action for #1151
Bump version to 9.3.40
Bump version to 9.3.40-dev
Tweak threadcount again; #1151
Bump version to 9.3.41
Bump version to 9.3.41-dev
Move min_threads out of py into env; #1151

We need to be able to tweak this in heroku config, not requiring a
redeploy.
Bump version to 9.3.42
Bump version to 9.3.42-dev
fixed no method error showFeedback