re: GitHub Pages
- GitHub changed the default branch for new repositories to "main" instead of "master"
- Reworded some rections to clarify the intent and/or process
- Changed a note into a NOTE: section
- Unified word usage between the Project and User/Organisation sections.  
  This also changes/fixes the title for Organisations/Users, as the order of these to words was reversed from the text below.

Replace more references to the `master` branch with references to the `main` branch, as per recent and new standard for new repositories by GitHub.

Organisation changed to Organization, in accordance with other spellings of the word.