message: Add a simple example to the README
diff: A declarative data definition language for formally specifying sound binary
  data formats.
  +## Example
  +
  +```plain
  +Bitmap = struct {
  + width: u16le,
  + height: u16le,
  + data: [u8; width * height],
  +};
  +```
  +
  ## Goals
  Here is a list of lofty goals that we would like to guide our work:
  