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
Merge branch '3.0' of https://github.com/spf13/spf13-vim into 3.0
remove some unused plugins & add Tern/Dockerfile
check for modifications outside vim
CtrlSpace config change
remove unused config
bring back NERDTree bookmarks
Tweak Vim-Over config
remove some EasyMotion mappings that were getting annoying
revert to default Wildfire mappings for now