Add JS based pulling in of issue counts with d:1 easy in getting started as a dev guide

[orta]

on http://guides.cocoapods.org/contributing/dev-environment.html with URLS like https://github.com/CocoaPods/CocoaPods/issues?q=is%3Aopen+is%3Aissue+label%3Ad1%3Aeasy for each gem.

[segiddins]

Can probably use https://developer.github.com/v3/issues/#list-issues-for-a-repository

[endocrimes]

@orta That would be pretty handy, might be worth filtering by not s4/s5 as well?

[fabiopelosin]

:metal:

[orta]

yeah, for sure.