message: Add docs for the new helper functions
diff: @@ -346,11 +346,15 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  Ok(())
  }
  + /// Helper function to read an OsString from a null-terminated sequence of bytes, which is what
  + /// the Unix APIs usually handle.
  fn read_os_string_from_c_string(&mut self, scalar: Scalar<Tag>) -> InterpResult<'tcx, OsString> {
  let bytes = self.eval_context_mut().memory.read_c_str(scalar)?;
  Ok(bytes_to_os_str(bytes)?.into())
  }
  + /// Helper function to write an OsStr as a null-terminated sequence of bytes, which is what
  + /// the Unix APIs usually handle.
  fn write_os_str_to_c_string(&mut self, os_str: &OsStr, ptr: Pointer<Tag>, size: u64) -> InterpResult<'tcx> {
  let bytes = os_str_to_bytes(os_str)?;
  let len = bytes.len();
  