refactor(seek) explain why seek to sample works

src/decoder/vorbis.rs

@@ -78,6 +78,7 @@ where
 
     #[inline]
     fn try_seek(&mut self, pos: Duration) -> Result<(), SeekError> {
+        // note sample rate in vorbis encoding is constant
         let samples = pos.as_secs_f32() * self.sample_rate() as f32;
         self.stream_reader.seek_absgp_pg(samples as u64)?;