Update Bitly link for meeting agenda doc

[scottrigby]

https://bit.ly/cncf-contribstrat-agenda—on the README and website—links to the Old CNCF TAG Contributor Strategy Notes Google doc. That doc has this redirect note at the top:

These are the historical meeting notes. Current meeting notes are in the new location.

Not sure who owns the Bitly account (I didn't see a note about that in the repo anywhere), so opening a general issue to update https://bit.ly/cncf-contribstrat-agenda from the old notes doc at https://docs.google.com/document/d/1Xjw-yAqidQW67zv7OfMRErsfCotc-mfQ_248Te_YL0g/edit to the new one at https://docs.google.com/document/d/1QKRyr5CNXx5Uc1nzMlyTq-gRKCIrBiYWGsiRZu_Dmyc/edit.