Add Self handbook (#2001)

The official [Self language](http://www.selflanguage.org/) documentation.

free-programming-books.md

@@ -165,6 +165,7 @@
 * [Scilab](#scilab)
 * [Scratch](#scratch)
 * [Sed](#sed)
+* [Self](#self)
 * [Smalltalk](#smalltalk)
 * [Spark](#spark)
 * [SQL (implementation agnostic)](#sql-implementation-agnostic)
@@ -2018,6 +2019,11 @@ For resources on Angular, Backbone, D3, Dojo, Ember, Express, jQuery, Knockout,
 * [Sed - An Introduction and Tutorial](http://www.grymoire.com/Unix/Sed.html)
 
 
+### Self
+
+* [The Self Handbook](http://handbook.selflanguage.org/current/)
+
+
 ### Smalltalk
 
 * [Computer Programming using GNU Smalltalk](http://www.canol.info/books/computer_programming_using_gnu_smalltalk/) (PDF)