Update src/Http/Http/src/BindingAddress.cs

Adding additional help message.

Co-authored-by: Günther Foidl <[email protected]>

Author: h5aaimtron

src/Http/Http/src/BindingAddress.cs

@@ -220,7 +220,7 @@ public static BindingAddress Parse(string address)
                 }
                 else
                 {
-                    throw new FormatException($"Invalid port: '{portString}'");
+                    throw new FormatException($"Invalid port: '{portString}, only numbers are allowed'");
                 }
             }