Add extracted source directory and README navigation

extracted-source/node_modules/pngjs/lib/paeth-predictor.js

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+"use strict";
+
+module.exports = function paethPredictor(left, above, upLeft) {
+  let paeth = left + above - upLeft;
+  let pLeft = Math.abs(paeth - left);
+  let pAbove = Math.abs(paeth - above);
+  let pUpLeft = Math.abs(paeth - upLeft);
+
+  if (pLeft <= pAbove && pLeft <= pUpLeft) {
+    return left;
+  }
+  if (pAbove <= pUpLeft) {
+    return above;
+  }
+  return upLeft;
+};