add docs for add_filter
add docs for add_filter

mwpastore/sinatra,ryanshaw/sinatra,mwpastore/sinatra,ryanshaw/sinatra,sinatra/sinatra,JonMidhir/sinatra,jkowens/sinatra,jkowens/sinatra,mwpastore/sinatra,sinatra/sinatra,burningTyger/sinatra,JonMidhir/sinatra,JonMidhir/sinatra,burningTyger/sinatra,jkowens/sinatra,burningTyger/sinatra