Show how to update the list of available Ruby versions
Show how to update the list of available Ruby versions

It wasn't clear how to update the list of installable Ruby versions after installing rbenv from Git. This is a bit confusing for people who use rbenv to run third party Ruby apps rather than write their own and are less likely to know/care about the distinction between `rbenv` and `ruby-build`. I hadn't touched it for about 2 years and totally forgot that I'd need to manually update ruby-build.

Alternatively, it might be better to make ruby-build a git submodule.
jrolfs/nodenv,nodenv/nodenv,rbenv/rbenv,jasonkarns/rbenv,jrolfs/nodenv,OiNutter/nodenv,OiNutter/nodenv,sstephenson/rbenv,nodenv/nodenv,rbenv/rbenv,sstephenson/rbenv,jasonkarns/rbenv,jasonkarns/rbenv,sstephenson/rbenv