docs(manipulate-entries): add usage section

subjects/manipulate-entries/README.md

@@ -8,7 +8,7 @@ Create 3 functions which work like the `.filter`, `.map` and `.reduce` array met
 - `mapEntries`: changes the key, the value or both.
 - `reduceEntries`: reduces the entries.
 
-Create 3 additional functions that use your previously created functions:
+Create 3 additional functions that use your previously created functions and take an object as input:
 
 - `totalCalories`: that will return the total calories of a cart.
 - `lowCarbs`: that leaves only those items which are lower than 50grams.
@@ -35,6 +35,58 @@ const nutritionDB = {
 }
 ```
 
+### Usage
+
+Here is a possible script to test your functions:
+
+```js
+const groceriesCart = { orange: 500, oil: 20, sugar: 480 }
+
+console.log('Total calories:')
+console.log(totalCalories(groceriesCart))
+console.log('Items with low carbs:')
+console.log(lowCarbs(groceriesCart))
+console.log('Total cart nutional facts:')
+console.log(totalCart(groceriesCart))
+```
+
+And its output:
+
+```console
+Total calories:
+2112.2
+Items with low carbs:
+{ oil: 20 }
+Total cart nutional facts:
+{
+  orange: {
+    calories: 245,
+    protein: 4.5,
+    carbs: 65,
+    sugar: 45,
+    fiber: 1,
+    fat: 0.5
+  },
+  oil: {
+    calories: 9.6,
+    protein: 0,
+    carbs: 0,
+    sugar: 24.6,
+    fiber: 0,
+    fat: 30.2
+  },
+  sugar: {
+    calories: 1857.6,
+    protein: 0,
+    carbs: 480,
+    sugar: 480,
+    fiber: 0,
+    fat: 0
+  }
+}
+
+```
+
 ### Notions
 
 - [filter](https://devdocs.io/javascript/global_objects/array/filter)