Add documentation about the barclamp cleanup for dev switch and dev checkout.
Add documentation about the barclamp cleanup for dev switch and dev checkout.

dev switch and dev checkout will now set any barclamps that are not
referenced as submodules in the target git branch to an empty branch.

This empty branch includes a README file describing that the barclamp
is intentionally empty.

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