Add documentation on configuring the language server

[milesziemer]

This entails two things:

1. Add a table for actual client-side configuration options that get sent during initialize
2. Add documentation on the build files the language server knows about. The language server looks for smithy-build.json and .smithy-project.json to find the roots of projects, and loads the smithy files specified in their sources/imports. smithy-build.json config can just point to the corresponding page on the Smithy docs, but we can have a table for the layout of the .smithy-project.json file, and suggestions on how to use it (i.e. when you're not using a smithy-build.json).