Wrong link to "Form of the Book" on resources page

[kaspermeyer]

The link to "Form of the Book" incorrectly points to "Grid Systems in Graphic Design" on Amazon.

I was about to submit a pull request, when I realized all the links has your nickname embedded in them @mrmrs. I didn't want to mess it up, in case it's an affiliate program of some sorts.

Let me know if the embedded nickname is irrelevant, and I'll go ahead and submit the pull request.