Move documentation from tensorflow.org

[codesue]

What happened?

Now that Model Card Toolkit is a community project, guides and API documentation will be removed from tensorflow.org and hosted elsewhere. There will still be an overview of MCT on tensorflow.org, and it will link to the new documentation site.

What is the expected behavior?

There should be a Model Card Toolkit documentation website that's separate from tensorflow.org.

To make this happen, we need to:

• Choose a platform (e.g. Read the Docs) since GitHub Pages is not enabled for this organization
• Choose a documentation tool (e.g. Sphinx or MkDocs)
• Update existing documentation to work with the chosen tool
• Automate building the docs (e.g. add a workflow)
• Update the contributing guide

Resources:

• documentation directory
• script to generate API docs
• TensorFlow documentation contribution guide and subsite template (helpful for understanding the current setup)