Document setting X-Frame-Options for template errors

Author: Ben Dickinson

docs/getting-started.md

@@ -58,6 +58,15 @@ TEMPLATES = [
 ]
 ```
 
+To see the detailed error pages generated by Django when you have `DEBUG = True` in the pattern library, you'll need to make sure you have `X_FRAME_OPTIONS` set, or your browser will block the response:
+
+```python
+if DEBUG:
+    X_FRAME_OPTIONS = "SAMEORIGIN"
+```
+
+Be careful only to change this when `DEBUG = True` unless you know what you're doing, you risk making your app less secure otherwise!
+
 ### Pattern library settings
 
 Still in Django settings, set the [`PATTERN_LIBRARY`](./reference/api.md#pattern_library) setting. Here is an example showing the defaults: