adds currency converter

learning_python3.md

@@ -458,6 +458,8 @@ That's not a number I understand...
 ```
 <details>
   <summary>Spoiler warning</summary>
+
+```python
 result = input("How much EUR would you like to convert into DOLLAR? ")
 
 rate = 1.14
@@ -468,6 +470,7 @@ if result.isdigit():
     print("{} EUR is {} DOLLAR".format(eur, dollar))
 else:
     print("That's not a number I understand...")
+```
 
 </details>