Documentation: Add v3 grpc C# client to libraries

Documentation/integrations.md

@@ -94,6 +94,7 @@
 
 - [wangjia184/etcdnet](https://github.com/wangjia184/etcdnet) - Supports v2
 - [drusellers/etcetera](https://github.com/drusellers/etcetera)
+- [shubhamranjan/dotnet-etcd](https://github.com/shubhamranjan/dotnet-etcd) - Supports v3+ (GRPC only)
 
 **PHP Libraries**