Rename mentions of `master` to `main`

[jwong-fs]

Under the section "Pushing Changes", the main branch is referred as the outdated name of master.

Acceptance criteria:

• Rename any instances of master to main

[msscsh]

You also need to bring this repository into default.
To do this, you need to remove the "master" branch and create the "main" branch starting from the HEAD of "gh-pages".

The PR #188 is correct

[jxu]

Most projects still have a master branch. main is just the virtue signalling GitHub name they introduced a few years ago.

[msscsh]

Too small a change for a very big discussion