Add rpcmiddleware config for remote lnd instance

Add rpcmiddleware.enable=true as a needed config for the remote lnd node

Author: lukeroberts

doc/config-lnd-remote.md

@@ -11,6 +11,7 @@ file contains the following additional configuration settings:
 ```text
 tlsextraip=<externally-reachable-ip-address>
 rpclisten=0.0.0.0:10009
+rpcmiddleware.enable=true
 ```
 
 Copy the following files that are located in your `~/.lnd/data/chain/bitcoin/mainnet`