Added books in slovak language

README.md

@@ -47,6 +47,7 @@ It's [easy](https://github.com/vhf/free-programming-books/wiki/Contribution). Pl
 + Portuguese (Portugal): [github](/free-programming-books-pt_PT.md)
 + Romanian (Romania): [github](/free-programming-books-ro.md)
 + Russian: [github](/free-programming-books-ru.md)
++ Slovak: [github](/free-programming-books-sk.md)
 + Spanish: [github](/free-programming-books-es.md)
 + Turkish: [github](/free-programming-books-tr.md)
 + Ukrainian: [github](/free-programming-books-ua.md)

free-programming-books-sk.md

+### Index
+* [Language Agnostic](#language-agnostic)
+    * [Právo](#pravo)
+
+
+### Language Agnostic
+#### Právo
+* [Zodpovednosť na internete](https://knihy.nic.cz/) - Zodpovednosť na internete (PDF)