Tweak the error message

src/briefcase/platforms/macOS/__init__.py

@@ -686,10 +686,18 @@ def notarize(self, filename, team_id):
                         store_credentials = True
                     else:
                         raise BriefcaseCommandError(
-                            f"""Unable to submit {filename.relative_to(self.base_path)} for notarization.
-                                To examine this failure use `xcrun notarytool history` to find the submission-id,
-                                then use `xcrun notarytool log <submission-id>` for a log of the error.
-                            """
+                            f"""\
+Unable to submit {filename.relative_to(self.base_path)} for notarization.
+To find the cause of this failure, get the submission ID by running:
+
+    xcrun notarytool history
+    
+Then run: 
+
+    xcrun notarytool log <submission-id>
+    
+to generate a full log of the error.
+"""
                         ) from e
         finally:
             # Clean up house; we don't need the archive anymore.