Clarify intention of the code that adds a default port

src/objective-c/GRPCClient/private/GRPCHost.m

@@ -58,8 +58,10 @@
 // Default initializer.
 - (instancetype)initWithAddress:(NSString *)address {
 
-  // To provide a default port, we try to interpret the address.
+  // To provide a default port, we try to interpret the address. If it's just a host name without
-  // TODO(jcanizales): Add unit tests for the types of addresses we want to let pass through.
+  // scheme and without port, we'll use port 443. If it has a scheme, we pass it untouched to the C
+  // gRPC library.
+  // TODO(jcanizales): Add unit tests for the types of addresses we want to let pass untouched.
   NSURL *hostURL = [NSURL URLWithString:[@"https://" stringByAppendingString:address]];
   if (hostURL && !hostURL.port) {
     address = [hostURL.host stringByAppendingString:@":443"];