Build calendar entry is missing

[duglin]

From https://github.com/knative/docs/blob/master/community/WORKING-GROUPS.md when I try to go to the Build WG's meeting link: https://calendar.google.com/event?action=TEMPLATE&tmeid=MTBkb3MwYnVrbDd0djE0a2kzcmpmbjZndm9fMjAxODA5MTJUMTcwMDAwWiBqYXNvbmhhbGxAZ29vZ2xlLmNvbQ&tmsrc=jasonhall%40google.com&scp=ALL I see other Knative meetings on there but not build's. It could be me though, sometimes thing go funky for me w.r.t. calendaring.

Proposal: add build to the knative calendar