[zshrc] autostart tmux with zsh
[zshrc] remove virtualenvwrapper plugin

The virtualenvwrapper plugin uses the lazy load virtualenvwrapper
script, which seems to crash zsh when autocompleting. The non-lazy
load script seems to work fine, so I'm using that instead.
[zshrc] adding the brew plugin
[zshrc] enable time stamp in history command
[install] mention recommended iTerm2 settings.
[install] remove install check for git and zsh.
[install] remove some blank lines.