Add release notes to changelog

docs/en/04_Changelogs/rc/3.4.0-rc1.md

@@ -1,5 +1,38 @@
 # 3.4.0-rc1
 
+## Upgrading notes
+
+Upgrading from 3.3 to 3.4 shouldn't require any code changes.
+
+Note that if you are upgrading from 3.1, you should review the [3.2 upgrade notes](3.2.0).
+
+### Other changes to be aware of
+
+These changes are unlikely to affect your upgrade, but we've noted them just in case you had unusual project code that
+was affected by these:
+
+ * When FormFields are rendered, leading & trailing whitespace is now stripped. The resulting HTML for form fields is
+   the same for the default fields, but if you have a custom form field that is relying on trailing whitespace being
+   outputted.
+ * DataObject::isChanged() now defaults to only checking database fields. If you rely on this method
+   for checking changes to non-db field properties, use getChangedFields() instead.
+   
+### Error handling
+
+Up until 3.4.0 error responses handled by SilverStripe have normally returned HTTP 200. The correct http response
+code can be turned on by setting `Debug.friendly_error_httpcode` config to true. This option will be removed in
+4.0 and fixed to always on.
+
+
+	:::yaml
+	---
+	Name: mydebug
+	---
+	Debug:
+  	  friendly_error_httpcode: true
+
+
+
 <!--- Changes below this line will be automatically regenerated -->
 
 ## Change Log