git-add: update to -A option (#1051)

See: (`git add -A` vs `git add .`)[http://stackoverflow.com/questions/26042390/git-add-asterisk-vs-git-add-period]

pages/common/git-add.md

@@ -8,7 +8,7 @@
 
 - Add all files (tracked and untracked):
 
-`git add .`
+`git add -A`
 
 - Only add already tracked files: