add optimism sepolia (#156)

Author: Dev Kalra

pages/entropy/contract-addresses.mdx

@@ -15,6 +15,7 @@ Entropy is available on the following EVM testnets:
 | base-goerli            | `0x4374e5a8b9C22271E9EB878A2AA31DE97DF15DAF` | `0x6CC14824Ea2918f5De5C2f75A9Da968ad4BD6344` |
 | fantom-sonic           | `0xb27e5ca259702f209a29225d0eDdC131039C9933` | `0x6CC14824Ea2918f5De5C2f75A9Da968ad4BD6344` |
 | blast-testnet          | `0x98046Bd286715D3B0BC227Dd7a956b83D8978603` | `0x6CC14824Ea2918f5De5C2f75A9Da968ad4BD6344` |
+| optimism-sepolia       | `0xdF21D137Aadc95588205586636710ca2890538d5` | `0x6CC14824Ea2918f5De5C2f75A9Da968ad4BD6344` |
 </div>
 
 The Fortuna URL for the default providers above is `https://fortuna-staging.pyth.network/v1/chains/<chain>`,