Improve git configuration

Author: andyone

.gitconfig

@@ -25,7 +25,8 @@
   ci = commit
   br = branch
   co = checkout
-  df = diff --staged
+  df = diff
+  dfs = diff --staged
   lg = log --color --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit
 
 [gitflow "branch"]