Add some notes on adding bundles.
Squashed 'dotvim/bundle/vim-sensible/' content from commit fee5928

git-subtree-dir: dotvim/bundle/vim-sensible
git-subtree-split: fee5928dc8650ed1ac0fccb160e4d89e4045bdc2
Merge commit 'dce0a2564c12be4dedd07ab826d0c853d80274fb' as 'dotvim/bundle/vim-sensible'