change default branch from master to main

[jessebot]

Is this a request for help?: kind of?

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Is this a BUG REPORT or FEATURE REQUEST? (choose one): feature request

Please change the name of the default branch from master to main in order to be more inclusive.

Anything else we need to know:

Aside from the arguably most important reason outlined above, these terms are becoming less used and therefore increasingly less compatible as more communities move away from its use (eg [NIST], [Python], [Drupal], [Github] and [Django]. The usage of 'master' and 'slave' in hardware and software has been halted by the Los Angeles County Office of Affirmative Action, the Django community, the Python community and several other programming languages. This was done because the language is offensive and hurts people in the community [Django2]. Root operator Internet Systems Consortium also stopped using the terms [ISC].
-- ref: ietf - draft-knodel-terminology-13

Another example of a repo that's taken these steps is docker/compose.