[Currency Exchange]: Update stub & exemplar with Module Docstring (#3600

)

* [Currency Exchange]:  Update stub with Module Docstring

Sub file was missing a docstring and tripping a "missing module docstring" warning in the Analyzer.

* [Currency Exchange]: Update exemplar.py

Added same docstring to exemplar file that was added to the stub file.

* Update exchange.py removed numeric stack doc

* Update exemplar.py 

Removed numeric stack doc.

[no important files changed]

exercises/concept/currency-exchange/.meta/exemplar.py

@@ -1,3 +1,10 @@
+"""Functions for calculating steps in exchaning currency.
+
+Python numbers documentation: https://docs.python.org/3/library/stdtypes.html#numeric-types-int-float-complex
+
+Overview of exchanging currency when travelling: https://www.compareremit.com/money-transfer-tips/guide-to-exchanging-currency-for-overseas-travel/
+"""
+
 def exchange_money(budget, exchange_rate):
     """
 

exercises/concept/currency-exchange/exchange.py

@@ -1,3 +1,12 @@
+"""Functions for calculating steps in exchaning currency.
+
+Python numbers documentation: https://docs.python.org/3/library/stdtypes.html#numeric-types-int-float-complex
+
+Overview of exchanging currency when travelling: https://www.compareremit.com/money-transfer-tips/guide-to-exchanging-currency-for-overseas-travel/
+"""
+
+
+
 def exchange_money(budget, exchange_rate):
     """