Add explanatory note

Author: chrisdavidmills

api/ReportingObserver.json

@@ -179,7 +179,8 @@
                 ],
                 "support": {
                   "chrome": {
-                    "version_added": "145"
+                    "version_added": "145",
+                    "notes": "The `crash` reporting type can be specified in the `types` array, but crash reports are not observed by reporting observers. They can be sent to reporting endpoints."
                   },
                   "chrome_android": "mirror",
                   "edge": "mirror",