message: Added link for unexplained topic in the book.
  Stack overflow link added for why we need to multiply normal with the transpose of the inverse of transformation matrix. Makes easy for beginners to navigate to the problem.
diff: @@ -64,7 +64,7 @@ void main() {
  We also need to multiply the normal by the matrix, but the transformations are a bit different
  and the calculation a bit weird. Since I didn't go into details about how matrices work,
  -I won't go into details about why you have to use the transpose of the inverse.
  +I won't go into details about why you have to use the transpose of the inverse ([click for details](https://stackoverflow.com/q/13654401)).
  If you recall the section about colors, the attributes that we pass from the vertex shader
  to the fragment shader are interpolated per fragment. This means that each fragment will get
  