Update CONTRIBUTING.md
Update CONTRIBUTING.md

I know it's cheesy to update a .md for hacktoberfest but I have been dying to put some things in here and to switch some things around. Perhaps you'll disagree on the 'easiest way to build the source code' but I wanted to invert the two because I find clicking lots easier.
marcemarc/Umbraco-CMS,arknu/Umbraco-CMS,marcemarc/Umbraco-CMS,marcemarc/Umbraco-CMS,tcmorris/Umbraco-CMS,abryukhov/Umbraco-CMS,hfloyd/Umbraco-CMS,bjarnef/Umbraco-CMS,robertjf/Umbraco-CMS,abjerner/Umbraco-CMS,umbraco/Umbraco-CMS,bjarnef/Umbraco-CMS,madsoulswe/Umbraco-CMS,hfloyd/Umbraco-CMS,mattbrailsford/Umbraco-CMS,leekelleher/Umbraco-CMS,robertjf/Umbraco-CMS,robertjf/Umbraco-CMS,abryukhov/Umbraco-CMS,tcmorris/Umbraco-CMS,abryukhov/Umbraco-CMS,abjerner/Umbraco-CMS,mattbrailsford/Umbraco-CMS,hfloyd/Umbraco-CMS,umbraco/Umbraco-CMS,leekelleher/Umbraco-CMS,dawoe/Umbraco-CMS,arknu/Umbraco-CMS,bjarnef/Umbraco-CMS,abjerner/Umbraco-CMS,tcmorris/Umbraco-CMS,KevinJump/Umbraco-CMS,marcemarc/Umbraco-CMS,madsoulswe/Umbraco-CMS,KevinJump/Umbraco-CMS,umbraco/Umbraco-CMS,tcmorris/Umbraco-CMS,madsoulswe/Umbraco-CMS,JimBobSquarePants/Umbraco-CMS,bjarnef/Umbraco-CMS,arknu/Umbraco-CMS,JimBobSquarePants/Umbraco-CMS,KevinJump/Umbraco-CMS,marcemarc/Umbraco-CMS,leekelleher/Umbraco-CMS,mattbrailsford/Umbraco-CMS,dawoe/Umbraco-CMS,JimBobSquarePants/Umbraco-CMS,leekelleher/Umbraco-CMS,abryukhov/Umbraco-CMS,robertjf/Umbraco-CMS,mattbrailsford/Umbraco-CMS,abjerner/Umbraco-CMS,dawoe/Umbraco-CMS,leekelleher/Umbraco-CMS,robertjf/Umbraco-CMS,umbraco/Umbraco-CMS,dawoe/Umbraco-CMS,JimBobSquarePants/Umbraco-CMS,KevinJump/Umbraco-CMS,dawoe/Umbraco-CMS,NikRimington/Umbraco-CMS,arknu/Umbraco-CMS,KevinJump/Umbraco-CMS,JimBobSquarePants/Umbraco-CMS,tcmorris/Umbraco-CMS,NikRimington/Umbraco-CMS,NikRimington/Umbraco-CMS,hfloyd/Umbraco-CMS,hfloyd/Umbraco-CMS,tcmorris/Umbraco-CMS