add TLA book by Leslie Lamport

free-programming-books.md

@@ -1640,10 +1640,15 @@ See also [TeX](#tex)
 
 See also [LaTeX](#latex)
 
+
 ###Tizen
 * [Tizen for Dummies](https://developer.tizen.org/sites/default/files/blogs/tizenfordummiesmainchangelist.pdf) (PDF) by Jon Lansdell, Cheng Luo, Michelle Somersville
 
 
+###TLA
+* [Specifying Systems: The TLA+ Language and Tools for Hardware and Software Engineers](http://research.microsoft.com/en-us/um/people/lamport/tla/book.html) (Postscript or PDF) by Leslie Lamport
+
+
 ###TypeScript
 * [TypeScript for C# Programmers](http://www.infoq.com/minibooks/typescript-c-sharp-programmers)
 * [TypeScript Succinctly, Syncfusion](http://www.syncfusion.com/resources/techportal/ebooks/typescript) (PDF, Kindle) *(Just fill the fields with any values)*