add Real-World Example to Hash maps and Sets

Author: MarcoBasileDev

Cheatsheet/HashMapAndSets/hash_maps_and_sets.md

@@ -15,3 +15,9 @@
 
 - Hash maps: dictionary, counting frequencies, storing key-value pairs, quick lookups.
 - Hash sets: unique elements, marking elements as used or visited, check for duplicates.
+
+---
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+### Real-World Example
+
+Web browser cache: Hash maps and sets are used everywhere in real-words systems. A classic example of hash maps in action is in caching systems within web browsers. When you visit a website, your browser stores data such as images, HTML, and CSS files in a cache so it can load much faster on future visits.