Update README.markdown

Added information from this forum topic on how to add a bundle to the list: https://groups.google.com/forum/#!searchin/spf13-vim-discuss/install/spf13-vim-discuss/s_PMWxVVogM/otCEQs0ZlsYJ
Merge pull request #675 from jaguarondi/patch-1

Update README.markdown
Swapped out terryma/vim-multiple-cursors for the better supported kristijanhusak/vim-multiple-cursors
Merge pull request #691 from seyDoggy/3.0

Swapped vim-multiple-cursors
Merge branch '3.0' of https://github.com/spf13/spf13-vim into 3.0