Update contribution guide to encourage new features via plugins. [ci skip]
Update contribution guide to encourage new features via plugins. [ci skip]

crimsonknave/lita,sadiqmmm/lita,mcgain/lita,chriswoodrich/lita,sadiqmmm/lita,MatthewKrey/lita,litaio/lita,byroot/lita,brodock/lita,natesholland/lita,MatthewKrey/lita,jimmycuadra/lita,jaisonerick/lita,liamdawson/lita,crimsonknave/lita,mcgain/lita,byroot/lita,tristaneuan/lita,brodock/lita,liamdawson/lita,elia/lita,jimmycuadra/lita,natesholland/lita,jaisonerick/lita,chriswoodrich/lita,elia/lita,litaio/lita,tristaneuan/lita