readthedocs build fix

[hkershaw-brown]

Description:

• Added an explicit target for the welcome page (index.rst). The links to README.rst were relative using the filename, so had to be updated for the rename to index.rst.
• Using root_doc instead of master_doc to follow latest sphinx conf.py guidance
• explicit conf.py following readthedocs v2 configuration

Fixes issue

fixes #526

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation update

Documentation changes needed?

• [ ] My change requires a change to the documentation.
  • [ ] I have updated the documentation accordingly.

Tests

Tested the build on readthedocs: fix-doc-index branch build: https://readthedocs.org/projects/dart-documentation/builds/21507857/

Checklist for merging

• [ ] Updated changelog entry
• [ ] Documentation updated
• [ ] Update conf.py

Checklist for release

• [ ] Merge into main
• [ ] Create release from the main branch with appropriate tag
• [ ] Delete feature-branch

Testing Datasets

• [ ] Dataset needed for testing available upon request
• [ ] Dataset download instructions included
• [ ] No dataset needed

[mjs2369]

@hkershaw-brown everything looks great. I added some suggested changes to make the references to the Welcome page consistent (using "Getting Started" as the name), but feel free to ignore them.

I went through the docs to make sure all the references were working, and they are. So this is ready to merge into main once you either approve/reject the suggested changes, and then I'll approve the PR immediately afterwards

[hkershaw-brown]

@mjs2369 I can't see your suggestions.

Do you want to change the name of the label: .. _Welcome page: to .._Getting Started