Add note about CliMulti URL encoding to method docs.

core/CliMulti.php

@@ -51,7 +51,11 @@ class CliMulti {
      * If multi cli is not supported (eg windows) it will initiate an HTTP request instead (not async).
      *
      * @param string[]  $piwikUrls   An array of urls, for instance:
-     *                               array('http://www.example.com/piwik?module=API...')
+     *
+     *                               `array('http://www.example.com/piwik?module=API...')`
+     *
+     *                               **Make sure query parameter values are properly encoded in the URLs.**
+     *
      * @return array The response of each URL in the same order as the URLs. The array can contain null values in case
      *               there was a problem with a request, for instance if the process died unexpected.
      */