add both hashes to "Checksum mismatch"-Exception message

lib/sysgeneral.py

@@ -59,7 +59,10 @@ class SysGeneral:
                 readable_hash = hashlib.sha256(downloaded_content).hexdigest()
                 if expected_hash == readable_hash:
                     return
-                raise Exception("Checksum mismatch")
+                raise Exception(f"Checksum mismatch for file {os.path.basename(file_name)}:\n\
+expected: {expected_hash}\n\
+actual:   {readable_hash}\n\
+When in doubt, try deleting the file in question -- it will be downloaded again when running this script the next time")
 
         raise Exception("File checksum is not yet recorded")