More helpful warning when site url isn't correct

resources/frontend_client/index_template.html

@@ -33,7 +33,8 @@
                 }
 
                 if (actualRoot !== configuredRoot) {
-                    console.warn("Site URL root \"" + configuredRoot + "\" does not match actual root \"" + actualRoot + "\"");
+                    console.warn("Warning: the Metabase site URL basename \"" + configuredRoot + "\" does not match the actual basename \"" + actualRoot + "\".");
+                    console.warn("You probably want to update the Site URL setting to \"" + window.location.origin + actualRoot + "\"");
                     document.getElementsByTagName("base")[0].href = actualRoot;
                 }