Add info for proxy option mapping

Author: jitto

lib/mapping.js

@@ -666,7 +666,8 @@ var options = {
         /^(?:dot|spec|tap|xunit|list|progress|min|nyan|landing|json|doc|markdown|teamcity)$/,
     },
     proxy: {
-      name: "proxy"
+      name: "proxy",
+      info: "set the proxy used to fetch results",
     },
   },
   waterfall: {