feat: htan-docs

[aditigopalan]

Building docs to point to htan csv. Fixes #354

Changing #373 to point to HTAN.model.csv

Initial version of docs with homepage and dictionary. Fixes #354

To test locally

1. Install mkdocs, mkdocs-material mkdocs-table-reader-plugin, ideally in a virtual environment, e.g.

   conda create -n docs python=3.12
   conda activate docs
   pip install mkdocs mkdocs-material mkdocs-table-reader-plugin

2. Change directories to the repo and checkout this branch:

   cd path/to/data-models 
   git checkout htan-docs

3. Start the server:

   mkdocs serve

   This will serve the documentation on http://127.0.0.1:8000/home

Once done, stop the server with Ctrl + C