automation: remove the bit with ~ within a shell variable, since it didn't work.
automation: mention .bash_profile on Mac
automation: add link to discussion of .bashrc vs .bash_profile

 - still have Mac users edit .bash_profile rather than .bashrc,
   but point to the discussion of .bashrc vs .bash_profile (which also
   mentions the unique behavior on Macs).
Merge pull request #128 from kbroman/2014-08-25_automation_fixes

Thanks for the quick fixes!