feat(shopping): add new exercise

subjects/devops/shopping/README.md

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+# shopping
+
+## Instructions
+
+Create a file `shopping.py` with a function `remember_the_apple(shopping_list)`.
+
+This function input is a list of string, like this:
+
+```python
+['tomatoes', 'pastas', 'apple', 'salt']
+```
+
+If the string `'apple'` is not in the list, it should be added. The function return the updated list. If the apple is in the list, simply return it.
+
+If the input list is empty, the returned list should be also empty (don't add the apple in that case).
+
+## Usage
+
+Here is a possible `test.py` to test your functions:
+
+```python
+import shopping
+
+if __name__ == '__main__':
+    list_with_apple = ['tomatoes', 'pastas', 'apple', 'salt']
+    list_without_apple = ['tomatoes', 'pastas', 'salt']
+
+    print(shopping.remember_the_apple(list_with_apple))
+    print(shopping.remember_the_apple(list_without_apple))
+```
+
+```bash
+$ python test.py
+['tomatoes', 'pastas', 'apple', 'salt']
+['tomatoes', 'pastas', 'salt', 'apple']
+```
+
+## Notions
+
+- [lists](https://docs.python.org/3/tutorial/datastructures.html#)
+- [Conditions](https://docs.python.org/3/tutorial/datastructures.html#more-on-conditions)