message: Add a note describing the register naming convention in `raw_syscalls.rs` (for real this time).
diff: // RawSyscalls is designed to minimize the amount of handwritten assembly code
  // needed without generating unnecessary instructions. There are a few major
  // factors affecting its design:
  -// 1. Most system calls only clobber r0-r4, while yield has a far longer
  +// 1. Most system calls only clobber r0-r4 (*), while yield has a far longer
  // clobber list. As such, yield must have its own assembly
  // implementation.
  // 2. The compiler is unable to optimize away unused arguments. For example,
  // ABI, so probably true for the Rust ABI), which are treated as
  // clobbered regardless.
  //
  +// (*) When this file refers to registers, it uses the same naming convention as
  +// the Tock 2.0 syscalls TRD. Registers r0-r4 correspond to ARM registers r0-r4
  +// and RISC-V registers a0-a4.
  +//
  // Currently, yield takes exactly one argument, to specify what yield type to
  // do. Therefore we only need one raw yield call.
  //
  