Add "Design With FontForge" (CC licensed)

There are also French and Chinese translations which can be added but the misc category doesn't exist in those lists.

Font design is on the boundary between design and programming. Hope there's room for this.

free-programming-books.md

@@ -458,6 +458,7 @@
 * [Computer Musings](http://scpd.stanford.edu/knuth/index.jsp) (lectures by Donald Knuth)
 * [CS For All](https://www.cs.hmc.edu/csforall/)
 * [Culture \& Empire: Digital Revolution](http://hintjens.com/books) (PDF)
+* [Design With FontForge](http://designwithfontforge.com/en-US/index.html)
 * [Designing for Performance](http://designingforperformance.com) - Lara Hogan
 * [Designing Interfaces](http://designinginterfaces.com) - Jennifer Tidwell
 * [DevDocs](http://devdocs.io) - Documents for Developers in 1 place