Add a link to /releases/
Add a link to /releases/

I'm new to CoreOS and had to go fishing around to find the /releases/ page to find out what alpha/beta mean to CoreOS. This adds a link so it's easy to find in context.
skynet/docs,iankronquist/docs,endocode/coreos-docs,mischief/coreos-docs,wli6/docs,jdloft/docs,ionave/docs,bq-xiao/docs,ksmaheshkumar/docs-2,robszumski/docs,mjg59/docs,hkjn/docs-1,atxwebs/docs,jonboulle/docs,coreos/docs,joshix/docs,marineam/coreos-docs,michelleN/docs