Renaming the Main Branch

[s2t2]

Right now the main branch is called "copybara_push", related to Google's Copybara tool, which syncs code between this public GitHub repo and Google's internal codebase.

However there is anecdotal evidence that this branch name is potentially confusing for open source collaborators.

It might be helpful to follow general open source conventions about branch naming, where by default the main branch is called "main".

[igopalakrishna]

@s2t2 I opened PR #139 to prep for the default-branch rename.

This PR only adds a TODO/note in mkdocs.yml so edit_uri can be updated from copybara_push -> main after the branch rename (to avoid breaking “Edit this page” links before main exists). It does not rename the branch itself.

Once the branch rename is done, we can flip edit_uri to edit/main/docs/ and verify Copybara still syncs correctly.

[s2t2]

OK thanks! I want to consider this more, and socialize the change with members of the working group. Moving this issue to the icebox for now until we are ready to pick it back up.