Paradox in CLA-signing procedure is barring new contributors

[floor-licker]

It used to be that to "sign" the CLA, you would submit a PR to the clabot-config repository whereby adding your GitHub username to the contributors list in the .clabot file counted as a signature for having read and agreed to the CLA. Now it seems that in submitting a PR to that repo, cla-bot responds telling you that you can't contribute to the repo until you've signed the CLA, i.e., you can't sign the CLA until you've signed the CLA.