Update DOC.md (#1148)

* Update DOC.md

* Update go/grpcweb/DOC.md

Co-authored-by: Johan Brandhorst-Satzkorn <[email protected]>

Co-authored-by: Johan Brandhorst-Satzkorn <[email protected]>

Author: AbdullahJanKhan

go/grpcweb/DOC.md

@@ -15,6 +15,7 @@ protocol specification.
 Here's an example of how to use it inside an existing gRPC Go server on a
 separate http.Server that serves over TLS:
 
+```go
     grpcServer := grpc.Server()
     wrappedGrpc := grpcweb.WrapServer(grpcServer)
     tlsHttpServer.Handler = http.HandlerFunc(func(resp http.ResponseWriter, req *http.Request) {
@@ -25,7 +26,7 @@ separate http.Server that serves over TLS:
     	// Fall back to other servers.
     	http.DefaultServeMux.ServeHTTP(resp, req)
     })
-
+```
 If you'd like to have a standalone binary, please take a look at `grpcwebproxy`.
 
 ## Usage