Added clarification to 'Using branches' in docs/contributing.txt

git-svn-id: http://code.djangoproject.com/svn/django/trunk@1762 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/contributing.txt

@@ -223,15 +223,22 @@ trunk more than once.
 Using branches
 --------------
 
-To test a given branch, you can simply check out the entire branch. Or, if
-you've got a working directory you'd like to switch to use a branch, you can
-use::
+To test a given branch, you can simply check out the entire branch, like so::
+
+    svn co http://code.djangoproject.com/svn/django/branches/<branch>/
+
+Or, if you've got a working directory you'd like to switch to use a branch,
+you can use::
 
     svn switch http://code.djangoproject.com/svn/django/branches/<branch>/
 
 ...in the root of your Django sandbox (the directory that contains ``django``,
 ``docs``, and ``tests``).
 
+The advantage of using ``svn switch`` instead of ``svn co`` is that the
+``switch`` command retains any changes you might have made to your local copy
+of the code. It attempts to merge those changes into the "switched" code.
+
 Official releases
 =================