examples: Explain reason for plainText()
diff --git a/examples/src/main/java/io/grpc/examples/helloworld/HelloWorldClient.java b/examples/src/main/java/io/grpc/examples/helloworld/HelloWorldClient.java
index e44b8b2..4b755da 100644
--- a/examples/src/main/java/io/grpc/examples/helloworld/HelloWorldClient.java
+++ b/examples/src/main/java/io/grpc/examples/helloworld/HelloWorldClient.java
@@ -51,6 +51,8 @@
   /** Construct client connecting to HelloWorld server at {@code host:port}. */
   public HelloWorldClient(String host, int port) {
     channel = ManagedChannelBuilder.forAddress(host, port)
+        // Channels are secure by default (via SSL/TLS). For the example we disable TLS to avoid
+        // needing certificates.
         .usePlaintext(true)
         .build();
     blockingStub = GreeterGrpc.newBlockingStub(channel);