Update README instructions

[LKedward]

Additional information required (thanks @vmagnin):

• Click on “Use this template > Create a new repository” (private, include all branches)
• In the settings of the new repository (Actions > General), set “Workflow permissions” to “read and write permission” instead of the default “read repository…” (and clicked on Save).
• Update the repo URLs in README.md and .github/workflows/CI.yml (LKedward/latex-github-collab => /)

[morganrivers]

Thanks for providing the template! I like it.
I do encourage you to simply paste those bullet points in the readme, it would have saved me another hour of fussing around :)

It seems like the creation of a "previews" branch may or may not be an additional necessary step?
I was a bit confused by that.
Once I made the "previews" branch, that seemed to fix things and now everything works now, so perhaps consider whether you want to add that to your readme as well.