README Clarity Updates

[T99]

Edits to the README to provide clarity on the use of the plugin without having to dive into the code. I willl admit, there wasn't much diving, but more obvious is always better.

Changes:

• Added short guide on Vundle installation to dispel the confusion that there is no support.
• Added example of what <Leader> is (I didn't know and I've been using vim for... a while).
• Added examples of the three over-arching commands that enable, disable, and toggle the plugin's main functionality.
  • Added example of the 'enable-by-default' option.

Resolves Issues:

• 105 How to use vim-indent-guides in my vim profiles?

• 123 Vundle support

• 126 install with vundle

• 127 Documentation for Enabling, Disabling, Toggling Plugin

[nathanaelkane]

Thanks for the PR @T99-, much appreciated :)

I squashed the commits, made a few small tweaks, and merged manually.