Added commit sign off section
Added commit sign off section

This was in the main contributing guidelines, but is only enforced in this repo. I've added it here.

As part of https://github.com/ipfs/community/issues/63

License: MIT
Signed-off-by: Richard Littauer <fcee8564704783f97ef9b85136372a5bdd496db6@gmail.com>

Quantomicus/go-ipfs,sahib/go-ipfs,ipfs-filestore/go-ipfs,chriscool/go-ipfs,kyledrake/go-ipfs,shadoxx/go-ipfs,RealImage/go-ipfs,RealImage/go-ipfs,locusf/go-ipfs,kpcyrd/go-ipfs,AtnNn/go-ipfs,MichaelMure/go-ipfs,MrSparc/go-ipfs,Quantomicus/go-ipfs,thelinuxkid/go-ipfs,kevina/go-ipfs,Luzifer/go-ipfs,Kubuxu/go-ipfs,shadoxx/go-ipfs,sahib/go-ipfs,juztamau5/go-ipfs,thelinuxkid/go-ipfs,moreati/go-ipfs,insionng/go-ipfs,JustinDrake/go-ipfs,rht/go-ipfs,Luzifer/go-ipfs,kyledrake/go-ipfs,AtnNn/go-ipfs,Quantomicus/go-ipfs,kpcyrd/go-ipfs,moreati/go-ipfs,bconfais/go-ipfs,AtnNn/go-ipfs,locusf/go-ipfs,bconfais/go-ipfs,Kubuxu/go-ipfs,kpcyrd/go-ipfs,csasarak/go-ipfs,chriscool/go-ipfs,tswindell/go-ipfs,llawall/go-ipfs,shadoxx/go-ipfs,WilliButz/go-ipfs,WilliButz/go-ipfs,insionng/go-ipfs,tswindell/go-ipfs,chriscool/go-ipfs,Luzifer/go-ipfs,csasarak/go-ipfs,kevina/go-ipfs,moreati/go-ipfs,tswindell/go-ipfs,kyledrake/go-ipfs,ianopolous/go-ipfs,kevina/go-ipfs,MrSparc/go-ipfs,juztamau5/go-ipfs,thelinuxkid/go-ipfs,rht/go-ipfs,RealImage/go-ipfs,Kubuxu/go-ipfs,MrSparc/go-ipfs,palkeo/go-ipfs,JustinDrake/go-ipfs,WilliButz/go-ipfs,csasarak/go-ipfs,MichaelMure/go-ipfs,bconfais/go-ipfs,OpenBazaar/go-ipfs,peersafe/go-ipfs,OpenBazaar/go-ipfs,ipfs-filestore/go-ipfs,insionng/go-ipfs,peersafe/go-ipfs,MichaelMure/go-ipfs,rht/go-ipfs,ianopolous/go-ipfs,peersafe/go-ipfs,locusf/go-ipfs,sahib/go-ipfs,JustinDrake/go-ipfs,llawall/go-ipfs,llawall/go-ipfs,ipfs-filestore/go-ipfs,juztamau5/go-ipfs,palkeo/go-ipfs,palkeo/go-ipfs,OpenBazaar/go-ipfs,ianopolous/go-ipfs