Revert "docs: remove dead Medium link from data availability page"

This reverts commit 97ee61d.

Author: randygrok

docs/learn/data-availability.md

@@ -5,6 +5,7 @@ Data availability (DA) is a core of Evolve's. Evolve utilize's  data availabilit
 Learn more about data availability:
 
 - [What is DA](https://celestia.org/what-is-da/)
+- [The importance of DA for Rollups](https://medium.com/zeeve/exploring-data-availability-layer-and-its-importance-in-rollups-0a4fbf2e0ffc)
 
 ## How Evolve Handles Data Availability