Add a basic description for CentOS adapted from the existing description and some basic copy from Wikipedia
Tweak the IRC language slightly by making it a separate paragraph

This is especially useful for READMEs where %%MAILING_LIST%% is actually plugged in, making a three-part list that we can't easily add an Oxford comma to.

Also, this allows us to explain that not all the image maintainers will necessarily be in that IRC channel ("You can also reach _many_ ...").
Merge pull request #53 from infosiftr/centos

Add a basic description for CentOS adapted from the existing description...
Merge pull request #54 from infosiftr/tweak-irc

Tweak the IRC language slightly by making it a separate paragraph
Run `./update.sh`
Update ubuntu to match Hub description
Add fedora with content from Hub
Update jruby tags