Set up ReadTheDocs documentation

[Ritesh313]

Set up a ReadTheDocs documentation site for NeonTreeClassification using a structure similar to https://deepforest.readthedocs.io/en/v1.5.0/getting_started/comparison.html.

Acceptance criteria:

• Documentation uses Sphinx (MyST or reStructuredText) and is deployed to ReadTheDocs.
• Structure includes sections for Getting Started, Usage, Dataloader, Pretrained Models, Tutorials, and API Reference.
• Add starter content for each page, leaving placeholders for detailed instructions and references.
• Include a TOC, navigation, and links to source code and notebooks if available.
• Integrate GitHub Actions for docs build if desired.

Future work:

• Each main docs page will be a sub-issue linked here for incremental contribution.
• Page-level instructions, examples, and tutorials will be added in child issues.

Parent: Next steps for the package (#4)