Updating what is a Subgraph (#133)

* Updating screenshot

* Updating what is a Subgraph

* Minor

Author: ahmadmardeni1

pages/en/developer/define-subgraph-hosted.mdx

@@ -2,7 +2,7 @@
 title: Define a Subgraph
 ---
 
-A subgraph defines which data The Graph will index from Ethereum, and how it will store it. Once deployed, it will form a part of a global graph of blockchain data.
+A subgraph defines which data The Graph will index from a blockchain, and how it will store it. Once deployed, it will form a part of a global graph of blockchain data which you can retrieve using GraphQL.
 
 ![Define a Subgraph](/img/define-subgraph.png)