git-add: update page (#12982)

Co-authored-by: spageektti <git@spageektti.cc>

pages/common/git-add.md

@@ -11,6 +11,10 @@
 
 `git add -A`
 
+- Add all files in the current folder:
+
+`git add .`
+
 - Only add already tracked files:
 
 `git add -u`