docs: Update C# grpc docs to use Grpc.Net.Client

The Grpc.Core NuGet package is in maintentance mode. Grpc.Net.Client is now the recommended implementation.

docs/grpc/java.md

@@ -102,6 +102,10 @@ In the build section,  we'll need to configure the following things :
 </build>
 ```
 #### Main.java
+Use the code below to set up a channel and client to connect to your `lnd` node.
+
+Note that when an IP address is used to connect to the node (e.g. 192.168.1.21 instead of localhost) you need to add `--tlsextraip=192.168.1.21` to your `lnd` configuration and re-generate the certificate (delete tls.cert and tls.key and restart lnd).
+
 ```java
 import io.grpc.Attributes;
 import io.grpc.CallCredentials;