update checkpoint sync description

setup-wizard.yml

@@ -16,10 +16,9 @@ fields:
       service: beacon-validator
     title: Gnosis chain node URL
     description: >-
-      Your Beacon chain node must have access to a syncronized gnosis chain node. 
-      If you have not already, make sure to install and sync a gnosis node of your choice.
-      Then, input the URL of the node that you wish to use or a remote one:
-      For example: https://rpc.xdaichain.com/
+      Your Beacon chain node must have access to a syncronized xdai mainnet node. 
+      If you have not already, make sure to install and sync an xdai node of your choice ([install nethermind gnosis](http://my.dappnode/#/installer/nethermind-xdai.dnp.dappnode.eth)) and use its RPC url
+      Or use the official one: https://rpc.xdaichain.com/
   - id: checkpointSyncUrl
     target:
       type: environment