message: Add basic build directions
  There's some invisible steps for the not deeply in-the-know
diff: # libtock-rs
  Rust userland library for Tock (WIP)
  +
  +## Getting Started
  +
  +This project is nascent and still under heavy development, but first steps:
  +
  +1. Get a copy of the latest nightly, in this repo's root:
  +
  + `rustup override set nightly`
  +
  +2. Need to grab a copy of the rust sources:
  +
  + `rustup component add rust-src`
  +
  +3. Now you should be able to build with:
  +
  + `xargo build --target thumbv7em-tock-eabi`
  