Add technical guide for JULES visibility change

[Pierre Siddall (Pierre-siddall)]

PR Summary

Code Reviewer: James Bruten (@james-bruten-mo)

This PR adds the technical guide for users to update their JULES fork after it is set to public visibility.

Code Quality Checklist

• I have performed a self-review of my own code
• I have locally built the documentation successfully, and the output of changed sections is as expected

Code Review

• The changes are coherent and valid

[James Bruten (james-bruten-mo)]

This also requires a few other changes. In FurtherDetails/index.rst you need to add the page to the toctree.

In source/git_faq.rst we already have the beginnings of an answer on this topic. That should be changed so it just points to this page. But it also contains a 2nd option about contacting github support. We should include that on the page as an alternative.

Finally, please double check the output of the build. As it currently is, is clearly not right which is easy to check.

[James Bruten (james-bruten-mo)]

Instead of bold facing the step headings, instead use #. will create a numbered list. So:

#. Create a new public fork
   
   * In order to do this you should first rename your existing fork, from the settings page of that fork.
   * Then :ref:`create a new fork <forking>`
   * This new fork will be public to match the MetOffice/Jules repository.

And then using #. similarly in the other steps

[James Bruten (james-bruten-mo)]

Please also copy/adapt the contact github support advice from https://github.com/MetOffice/simulation-systems/blob/main/source/git_faq.rst?plain=1#L53. Then the answer to that faq can just be modified to point at the new file, as in the recent changes

[James Bruten (james-bruten-mo)]

This needs to be #. not just a # to format correctly. You'll also need to indent the contained text and code block. See https://github.com/MetOffice/simulation-systems/blob/main/source/Reviewers/howtocommit.rst?plain=1#L179 for an example

[James Bruten (james-bruten-mo)]

A couple of final tweaks

[James Bruten (james-bruten-mo)]

Thanks, looks good now