Added book on Compiler Design (#5894)

Introduction to Compilers and Language Design - Douglas Thain (PDF)

books/free-programming-books-subjects.md

@@ -171,6 +171,7 @@ Books that cover a specific programming language can be found in the  [BY PROGRA
 * [Compiling Techniques (1969)](http://www.chilton-computing.org.uk/acl/literature/books/compilingtechniques/overview.htm) - F.R.A. Hopgood, Macdonald
 * [Crafting Interpreters (:construction:)](http://www.craftinginterpreters.com) - Bob Nystrom (HTML)
 * [Implementing Functional Languages: A Tutorial](http://research.microsoft.com/en-us/um/people/simonpj/Papers/pj-lester-book/) - Simon Peyton Jones, David Lester
+* [Introduction to Compilers and Language Design](https://www3.nd.edu/~dthain/compilerbook/compilerbook.pdf) - Douglas Thain (PDF)
 * [Let's Build a Compiler](http://www.stack.nl/~marcov/compiler.pdf) (PDF)
 * [Practical and Theoretical Aspects of Compiler Construction](http://web.stanford.edu/class/archive/cs/cs143/cs143.1128/) (class lectures and slides)
 * [The ANTLR Mega Tutorial](https://tomassetti.me/antlr-mega-tutorial/)