update readme

Author: calebdoxsey

README.md

@@ -4,6 +4,8 @@
 * bash - entries are added to `~/.bashrc`
 * fish - entries are added to `~/.config/fish/config.fish`
 * windows - entries are added to the registry for the current user
+* osx - entries are added to a user launchctl script. You will have to restart
+        programs to pick up the new environment. (ie restart your terminal)
 
 ## Installation
 `penv` is both a library and a command. To use the library in your own code see
@@ -27,6 +29,8 @@ Here's its usage:
         Permanently append VALUE to NAME in the environment
 
 ## Gotchas
+Windows requires at least Go 1.3.
+
 Different operating systems / shells aren't really compatible. I'm able to discern which environment variables I'm responsible for with shells (like bash) by using their config files, but I can't do that with Windows or OSX. All appends will get collapsed into sets, and unsets aren't just masking the value, they may actually remove it.
 
 In other words this command works but it's dangerous. If you set your `PATH` don't be surprised when it clears all the previous values and you can't get them back.