message: update linear to mel documentation
diff: @@ -104,6 +104,14 @@ def linear_to_mel_weight_matrix(num_mel_bins=20,
  `[0, sample_rate / 2]` into `num_mel_bins` frequency information from
  `[lower_edge_hertz, upper_edge_hertz]` on the [mel scale][mel].
  + This function follows the [Hidden Markov Model Toolkit
  + (HTK)](http://htk.eng.cam.ac.uk/) convention, defining the mel scale in terms of
  + a frequency in hertz according to the following formula:
  +
  + $$\textrm{mel}(f) = 2595 * \textrm{log}_{10}(1 + \frac{f}{700})$$
  +
  + In the returned matrix, all the triangles (filterbanks) have a peak value of 1.0.
  +
  For example, the returned matrix `A` can be used to right-multiply a
  spectrogram `S` of shape `[frames, num_spectrogram_bins]` of linear
  scale spectrum values (e.g. STFT magnitudes) to generate a "mel spectrogram"
  