Bug 1561433 [wpt PR 17508] - Added a link to spec to numbers-units-004 test, a=testonly

Automatic update from web-platform-tests
Added a link to spec to numbers-units-004 test (#17508)

--

wpt-commits: 288514517e5012ad4459c63e8b37e6dcff3fd561
wpt-pr: 17508

testing/web-platform/tests/css/CSS2/values/numbers-units-004.xht

@@ -4,6 +4,7 @@
         <title>CSS Test: Parsing integer numbers with '+'</title>
         <link rel="author" title="Microsoft" href="http://www.microsoft.com/" />
         <link rel="help" href="http://www.w3.org/TR/CSS21/syndata.html#numbers" />
+        <link rel="help" href="https://www.w3.org/TR/css-values-3/#integers" />
         <link rel="match" href="../reference/ref-filled-black-96px-square.xht" />
         <meta name="flags" content="" />
         <meta name="assert" content="Integers can be preceded by '+'." />
@@ -21,4 +22,4 @@
         <p>Test passes if there is a filled black square.</p>
         <div></div>
     </body>
-</html>
+</html>