Ggn0 add Pro Git it (#6377)

* Update free-programming-books-it.md

Add ProGit (it)

* check_urls=free-programming-books-it.md

check_urls=free-programming-books-it.md

* Update free-programming-books-it.md

Remove reverence to specific book version

* Update free-programming-books-it.md

Remove unnecessary links for `Pro Git` book formats

books/free-programming-books-it.md

@@ -17,6 +17,7 @@
   * [NoSQL](#nosql)
   * [Relazionali](#relazionali)
   * [SQL](#sql)
+* [Git](#git)
 * [Golang](#golang)
 * [HTML](#html)
 * [Java](#java)
@@ -120,6 +121,11 @@
 * [Progettare database NoSQL: la guida](http://www.html.it/guide/progettare-database-nosql/?cref=system) (HTML)
 
 
+#### Git
+
+* [Pro Git](https://git-scm.com/book/it) - Scott Chacon, Ben Straub (HTML, PDF, EPUB)
+
+
 #### NoSQL
 
 * [Guida MongoDB](http://www.html.it/guide/guida-mongodb/?cref=system) (HTML)