Small fixes to README.rst
Small fixes to README.rst

* Correct capitalization of the Python Package Index acronym
* Change `heldeup` to `held up`
WSDC-NITWarangal/gunicorn,mvaled/gunicorn,malept/gunicorn,tempbottle/gunicorn,ccl0326/gunicorn,ccl0326/gunicorn,prezi/gunicorn,MrKiven/gunicorn,harrisonfeng/gunicorn,gtrdotmcs/gunicorn,elelianghh/gunicorn,GitHublong/gunicorn,mvaled/gunicorn,1stvamp/gunicorn,gtrdotmcs/gunicorn,ephes/gunicorn,1stvamp/gunicorn,jamesblunt/gunicorn,gtrdotmcs/gunicorn,jamesblunt/gunicorn,malept/gunicorn,beni55/gunicorn,tejasmanohar/gunicorn,mvaled/gunicorn,z-fork/gunicorn,ccl0326/gunicorn,malept/gunicorn,keakon/gunicorn,1stvamp/gunicorn,zhoucen/gunicorn,zhoucen/gunicorn,prezi/gunicorn,jamesblunt/gunicorn,zhoucen/gunicorn,prezi/gunicorn