warn if IE8 is in compatibility mode

src/browser/ui/React.js

@@ -113,6 +113,16 @@ if (__DEV__) {
       }
     }
 
+    // If we're in IE8, check to see if we are in combatibility mode and provide
+    // information on preventing compatibility mode
+    if (document.documentMode && document.documentMode < 8) {
+      console.debug(
+        'Internet Explorer is running in compatibility mode, please add the following ' +
+        'tag to your HTML to prevent this from happening: ' +
+        '<meta http-equiv="X-UA-Compatible" content="IE=edge" />'
+      );
+    }
+
     var expectedFeatures = [
       // shims
       Array.isArray,