docs: update branch name in docs

[leavesster]

It appears that the default branch is set to master rather than main. The README and GitHub Actions configuration haven't been updated accordingly.

I have updated the documentation, but I've left the GitHub Actions branch as is to prevent any unnecessary approvals from GitHub Actions.

below is the github action branch which I do not update

https://github.com/camelot-dev/camelot/blob/master/.github/workflows/tests.yml

name: Tests

on:
  push:
    branches: [main]
  pull_request: