Merge pull request #495 from jboverfelt/master

Adding Erlang Handbook

free-programming-books.md

@@ -592,6 +592,7 @@
 * [Études for Erlang](http://chimera.labs.oreilly.com/books/1234000000726/index.html) - J. David Eisenberg
 * [Learn You Some Erlang For Great Good](http://learnyousomeerlang.com/) - Frederic Trottier-Hebert
 * [Concurrent Programming in ERLANG](http://www.erlang.org/download/erlang-book-part1.pdf)
+* [Erlang Handbook](https://github.com/esl/erlang-handbook/raw/master/output/ErlangHandbook.pdf) (PDF)
 
 
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