Add Vundle installation instructions

I added the syntax for installing this plugin via Vundle. Tested it on my system and it works.
Merge pull request #113 from m42e/master

Predefined command option for VimuxPromptCommand
Check for a predefined command for prompt before executing

VimuxPromptCommand was accepting 1 or more arguments instead of 0 or more. Vim
will complain about this despite nargs being set.
Merge pull request #114 from mxie/mx-fix-optional-prompt-arg

Check for a predefined command for prompt before executing
Added VimuxRunCommandInDir + doc
Merge pull request #112 from kavinderd/patch-1

Add Vundle installation instructions
Going back to formerly active directory after running command
fixed docs and added `:VimuxOpenRunner` command
Merge remote-tracking branch 'nikhgupta/feature/fix-docs'

Conflicts:
	doc/vimux.txt