[Documentation]: Full draw_tree documentation

[edwardchalstrey1]

Requested documentation improvement

• Adapt the tutorial notebooks to be full walkthroughs of the package features with clarity/narrative The tutorial added to PyGambit is already good, link to this
• Consider setting up a new sphinx/readthedocs myst/jupyterbook: https://jupyterbook.org/
• Integrate the existing EF specification PDF into these docs
• Completely replace README
• Add a gambit logo
• Add link to Gambit website
• Link to Gambit EFG spec

After merge of dt-docs branch to main:

• Action Required on GitHub: Once you push these changes to your main branch, you will need to go to your repository's Settings > Pages. Under the Build and deployment source, select "GitHub Actions". This will allow the new workflow to publish your site to https://gambitproject.github.io/draw_tree/
• Add link in Gambit docs to new DT docs
• Can we ensure PR previews are enabled?