doc: add a basic section `neobundle-migrate-from-pathogen`
doc: add a basic section `neobundle-migrate-from-pathogen`

This might be a good starting point for others.

jhchabran/neobundle.vim,payapayao/neobundle.vim,Shougo/neobundle.vim,netroby/vimsuite,TKNGUE/neobundle.vim,AndBicScadMedia/neobundle.vim