Update README.build to include an overview what happens during a build.
Update README.build to include an overview what happens during a build.

tserong/crowbar,mmnelemane/crowbar,nkrinner/crowbar,aspiers/crowbar,rsalevsky/crowbar,aplanas/crowbar,mmnelemane/crowbar,vwallfahrer/crowbar,rsalevsky/crowbar,aplanas/crowbar,crowbar/crowbar,rhafer/crowbar,rhafer/crowbar,SUSE-Cloud/crowbar,dirkmueller/crowbar,crowbar/crowbar,rhafer/crowbar,aspiers/crowbar,tserong/crowbar,dirkmueller/crowbar,vwallfahrer/crowbar,MaximilianMeister/crowbar,toabctl/crowbar,toabctl/crowbar,MaximilianMeister/crowbar,SUSE-Cloud/crowbar,nkrinner/crowbar