Clarification on which hooks can be suffixed

There are two files:
./hooks/after_install_auto_gem
./hooks/after_install_codesign

that aren't documented here. However, it's quite useful to have custom after_install scripts. Specifically to pre-install some useful gems, since .rvm/gemsets/default.gems and .rvm/gemsets/global.gems are usually overriten during `rvm update`.