Refactor readme with install descriptions

Made the instructions for setting up this environment a bit easier to understand and follow from a more basic level.
Hmmm weird. The new install script uses ~/.dotfiles.bak as the backup directory. Were you using the new script?

On Sun, Jul 20, 2014 at 1:06 PM, Austin Wood <notifications@github.com>
wrote:

>> @@ -11,15 +11,17 @@ Just some ZSH_IM_UX (zsh/vim/tmux) files to bask in the sun with.
>>  ### Install
>>  
>>      $ git clone --recursive https://github.com/ianks/Dotfiles ~/.dotfiles
>> +    $ mkdir dotfiles_old
> Whenever I tried to do this, I would always get a complaint that 'dotfiles_old is not a working directory'. You have to create the file yourself for it to move all of your old junk (if you have any).
> ---
> Reply to this email directly or view it on GitHub:
> https://github.com/ianks/Dotfiles/pull/3/files#r15151424