Rename default branch from master to main

[MarckK]

Hi all,

The CDF is in the process of changing all the default branches for repositories within cd foundation org from master to main.
Please see the discussion here: cdfoundation/foundation#409

I have unarchived this repo to change the default branch name to main and will soon re-archive the repo.

If any issues due to this change arise, please comment on this issue.

Thank you!