Added error handling

Author: cipherhacker

python/readme.md

@@ -15,4 +15,4 @@
  10. [User defined functions](./10-user_defined_functions.md)
  11. [Lambda](./11-Lambda.md)
  12. [Modules](./12-Modules.md)
- 13. [Error Handling]()
+ 13. [Error Handling](./13-Error_Handling.md)