Add Sphinx Documentation for ReadTheDocs

[medley56]

Context

The Curryer codebase is undeniably useful but we should support users by publishing documentation about installation, usage, and the scope of what the library does and doesn't do. This should include the top level README included on the front page of the docs, and subsections for users and developers who wish to contribute to the project.

Suggested Implementation

• Create a Sphinx build setup in the docs directory, using either rst or markdown for the documentation pages.
• Create sections in docs for user documentation and developer documentation (stubs for now).
• Add autogenerated API documentation using Sphinx autoapi or a similar extension to generate docs from docstrings in the codebase.
• Polish the README file to include a reference to the ReadTheDocs site, short description of the repo, and installation instructions.
• Link the GitHub project with ReadTheDocs to automatically publish documentation on push, including for PRs (ReadTheDocs supports this out of the box)