Update documentation and create static site

[adamjarling]

What does this do?

Adds a documentation, homepage, and static site solution to this Github repo.

Here's the contents of the /docs/README.md for more info.

This documentation uses Nextra. The documentation app is a NextJS app which lives in the /docs directory and is isolated from the rest of the root serverless-iiif project files.

Updating documentation

Navigate to the /docs directory, and run

# Install dependencies
npm install

# Start the app
npm dev

Generate static site docs

Run npm run build, which will output the static site in /docs/out.

[adamjarling]

@mbklein If you want to move forward with this, we should probably squash all the commits before merging.

[mbklein]

This looks great, @adamjarling! Thanks!