Add information about map scopes (#1368)

* Add information about map scopes

* Move "map scopes" info

README.md

@@ -1271,6 +1271,12 @@ expected as code is optimized and mappings are often simply not possible as
 some code no longer exists. For highest fidelity in source map debugging
 disable the `compress` option and just use `mangle`.
 
+When debugging, make sure you enable the **"map scopes"** feature to map mangled variable names back to their original names.  
+Without this, all variable values will be `undefined`. See https://github.com/terser/terser/issues/1367 for more details.
+<br/><br/>
+
+![image](https://user-images.githubusercontent.com/27283110/230441652-ac5cf6b0-5dc5-4ffc-9d8b-bd02875484f4.png)
+
 ### Compiler assumptions
 
 To allow for better optimizations, the compiler makes various assumptions: