fix(Themes): reword agnoster config (#58)

Themes.md

@@ -41,7 +41,7 @@ The rest of the themes, in alphabetical order:
 Additional setup:
 
 - Install one of the [patched fonts from Vim-Powerline](https://github.com/powerline/fonts) or [patch your own](https://github.com/powerline/fontpatcher) for the special characters.
-- *Optionally* set `DEFAULT_USER` to your regular username followed by prompt_context(){} in `~/.zshrc` to hide the “user@hostname” info when you’re logged in as yourself on your local machine.
+- *Optionally* set `DEFAULT_USER` to your regular username to hide the “user@hostname” info when you’re logged in as yourself on your local machine. Or add `prompt_context(){}` to `~/.zshrc` to always hide the “user@hostname” info.
 
 ### alanpeabody