Always show Custom image option (#328)

src/HasAssetField.php

@@ -12,7 +12,7 @@ trait HasAssetField
     protected static function getAssetFieldConfig()
     {
         if (! $container = config('statamic.seo-pro.assets.container')) {
-            return false;
+            return static::getAssetFieldContainerError();
         }
 
         return [
@@ -21,4 +21,24 @@ protected static function getAssetFieldConfig()
             'max_files' => 1,
         ];
     }
+
+    /**
+     * Show helpful asset field config error.
+     *
+     * @return array
+     */
+    protected static function getAssetFieldContainerError()
+    {
+        return [
+            'type' => 'html',
+            'html' => <<<'HTML'
+<div class="mt-2 text-sm text-red-500">
+    Asset container not configured.
+    <a class="text-red-500 underline" href="https://statamic.com/addons/statamic/seo-pro/docs#advanced-configuration" target="_blank">
+        Learn more
+    </a>
+</div>
+HTML,
+        ];
+    }
 }