add proper attributions for models

Author: cvalenzuela

src/PitchDetection/index.js

@@ -5,8 +5,8 @@
 
 /*
   Crepe Pitch Detection model
-  https://github.com/marl/crepe/tree/gh-pages
-  https://marl.github.io/crepe/crepe.js
+  Based on https://github.com/marl/crepe/tree/gh-pages
+  Original model and code: https://marl.github.io/crepe/crepe.js
 */
 
 import * as tf from '@tensorflow/tfjs';

src/Pix2pix/index.js

@@ -6,6 +6,8 @@
 /* eslint max-len: "off" */
 /*
 Pix2pix
+The original pix2pix Tensorflow implementation was made by affinelayer: github.com/affinelayer/pix2pix-tensorflow
+This version is heavily based on Christopher Hesse Tensorflow.js implementation: https://github.com/affinelayer/pix2pix-tensorflow/tree/master/server 
 */
 
 import * as tf from '@tensorflow/tfjs';

src/PoseNet/index.js

@@ -5,6 +5,7 @@
 
 /*
 PoseNet
+The priginal PoseNet model was ported to Tensorflow.js by Dan Oved.
 */
 
 import EventEmitter from 'events';

src/StyleTransfer/index.js

@@ -6,6 +6,8 @@
 /* eslint max-len: "off" */
 /*
 Fast Style Transfer
+This implementation is heavily based on github.com/reiinakano/fast-style-transfer-deeplearnjs by Reiichiro Nakano.
+The original Tensorflow implementation was developed by Logan Engstrom: github.com/lengstrom/fast-style-transfer 
 */
 
 import * as tf from '@tensorflow/tfjs';