Documentation prototype and ReadtheDocs CI

[bstefanuk]

This PR adds a prototype documentation site, along with necessary CI files, for hosting Tensile docs with ROCm styling. Currently, the docs are structured with a proposed format using placeholder files.

Local build steps:

1. Create a virtual environment: python3 -m venv .venv && source .venv/bin/activate
2. Install the Python packages needed to build the docs: pip3 install -r docs/sphinx/requirements.txt
3. Build the docs:

   cd docs
   python3 -m sphinx -T -b html -d _build/doctrees -D language=en . _build/html

4. Find the built docs in _build/html/

Notes:

• Each PR will build the documentation site as a job titled: docs/readthedocs.com:[project-id]