README: show how to define helper functions in a separate `module`
README: show how to define helper functions in a separate `module`

Developers might prefer to define helpers in a separate `module`, particularly
for modular apps, so let's provide an example in the docs.

Signed-off-by: Anurag Priyam <6e6ab5ea9cb59fe7c35d2a1fc74443577eb60635@gmail.com>

sinatra/sinatra,dariubs/sinatra,wzheng1/sinatra,frechei/sinatra,emiliocorpus/sinatra,nju520/sinatra,defsprite/sinatra,mwpastore/sinatra,Wirachmat/sinatra,d-bot/sinatra,nju520/sinatra,ksw2599/sinatra,nicoayala/sinatra,ktw1222/sinatra,cyberid41/sinatra,porras/sinatra,ktw1222/sinatra,midorineko/sinatra,kyontan/sinatra,sinatra/sinatra,ryanshaw/sinatra,blambeau/sinatra,autopp/sinatra,laplaceliu/sinatra,defsprite/sinatra,davydovanton/sinatra,miyazawatomoka/sinatra,trexnix/sinatra,eileencodes/sinatra,guidohcosta/sinatra,twanies/sinatra,QLGu/sinatra,JonMidhir/sinatra,kgrz/sinatra,Wirachmat/sinatra,jkowens/sinatra,sethuster/sinatra,lastcat/sinatra,trexnix/sinatra,DoraALin/sinatra,QLGu/sinatra,lastcat/sinatra,jenalgit/sinatra,JonMidhir/sinatra,gferguson-gd/sinatra,ganmacs/sinatra,kyontan/sinatra,howtolearntocode/sinatra,d-bot/sinatra,guidohcosta/sinatra,eileencodes/sinatra,cyberid41/sinatra,JonRowe/sinatra,JonRowe/sinatra,burningTyger/sinatra,DoraALin/sinatra,midorineko/sinatra,davydovanton/sinatra,Rayheng/sinatra,autopp/sinatra,Callygraphy/morrissey,marocchino/sinatra,RosenDimov/sinatra,mwpastore/sinatra,laplaceliu/sinatra,siberianbear/sinatra,jenalgit/sinatra,siberianbear/sinatra,burningTyger/sinatra,sethuster/sinatra,nicoayala/sinatra,miyazawatomoka/sinatra,ABaldwinHunter/sinatra-classic,porras/sinatra,mwpastore/sinatra,dariubs/sinatra,ABaldwinHunter/sinatra-classic,burningTyger/sinatra,ksw2599/sinatra,frechei/sinatra,JonMidhir/sinatra,ryanshaw/sinatra,emiliocorpus/sinatra,ganmacs/sinatra,RosenDimov/sinatra,wzheng1/sinatra,twanies/sinatra,bmizerany/sinatra,gferguson-gd/sinatra,kumji/sinatra,howtolearntocode/sinatra,jkowens/sinatra,Rayheng/sinatra,jkowens/sinatra,kumji/sinatra