I've made the switch from oh-my-zsh to prezto but I missed the default robbyrussell theme.
This is a close aproximation of that!
Like prezto prompt themes states:
A prompt theme is an autoloadable function file with a special name,
prompt_name_setup, placed anywhere in$fpath, but for the purpose of this project, themes should be placed in the modules/prompt/functions directory.
So to use this, just copy prompt_orgmir_setup to anywhere in $fpath and then add the following to zpreztorc:
zstyle ':prezto:module:prompt' theme 'orgmir'