Update README.md

Added hydra key back

Author: danielmain

README.md

@@ -40,7 +40,7 @@ Daedalus - Cryptocurrency Wallet
 
    substituters = https://cache.iog.io https://cache.nixos.org/
    trusted-substituters =
-   trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+   trusted-public-keys = hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
    
    # Only if using mac 
    extra-sandbox-paths = /System/Library/Frameworks /System/Library/PrivateFrameworks /usr/lib