Add note that ^ is a special character in windows.

branching/index.html

@@ -665,6 +665,9 @@ b7ae93b added from ruby
       front of the branch that we don't want to see.  For instance, if we want
       to see the commits that are in the 'erlang' branch that are not in the
       'master' branch, we can do <code>erlang ^master</code>, or vice versa.
+      Note that the Windows command-line treats <code>^</code> as a special
+      character, in which case you'll need to surround <code>^master</code>
+      in quotes.
     </p>
 
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