Better docs for altair-fastify-plugin

[jcollum-nutrien]

Is your feature request related to a problem? Please describe. The readme for altair-fastify-plugin could use more depth.

Describe the solution you'd like For instance:

app.register(AltairFastify, {
  /**
   * All these are the defaults.
   */
  path: '/altair',
  baseURL: '/altair/',
  endpointURL: '/graphql',
});

Why is path and baseURL the same path? What is the endpointURL for? If I start a server with these defaults what path do I navigate to to get to the Altair interface?

[imolorhe]

These are documented in the code https://github.com/altair-graphql/altair/blob/master/packages/altair-fastify-plugin/src/index.ts#L8-L25

I'd not want to have the documentation also in the README as that can get out of sync easily. We could consider using a tool to automatically generate the docs from the code, if this is necessary.

[kamatheuska]

Maybe we could write it down in the Altair Docs integrations page? https://altairgraphql.dev/docs/integrations/

I could do a PR if it is straithg forward enough :)

[imolorhe]

@kamatheuska Feel free to create a PR