Include references to install Yarn for building the UI, as well as the
alternative "docker-ui" make target.
The Yarn install process is currently dependent on yarn 1.x / pre-2.0
Update teleport build and dependencies setup instructions
* add notes about libfido and how to build tsh with it
* add detailed instructions about installing Go and Rust
* restructure/reformat the Local Build section
* add a note about TouchID support for tsh
* add instructions for test dependencies
* link to test dependencies from testing section of the README.md
* git submodule update note
* remove $ from shell command snippets
Co-authored-by: Alan Parra <alan.parra@goteleport.com>