Add links to branching slides

branching/branching.tex

@@ -549,9 +549,10 @@ Hit return to start merge resolution tool (meld):
 
     Zuotian Tatum
 
-    % https://www.atlassian.com/git
-
   \end{center}
+  \vfill
+  \permfoot{http://git-scm.com/book}\\
+  \permfoot{https://www.atlassian.com/git}
 \end{frame}
 
 \end{document}