Add documentation

Author: gammasoft71

README.md

@@ -358,7 +358,8 @@ public:
     auto message = co_await get_message();
     auto length = co_await get_size(message);
 
-    println("length : {}", length);
+    println("message : {}", message);
+    println("length  : {}", length);
     println("[main, thread {}] -> end", thread::current_thread().managed_thread_id());
   }
 
@@ -398,7 +399,8 @@ xtdc run
 
 ```
 [main], thread 1] -> start
-length : 13
+message : Hello, World!
+length  : 13
 [main, thread 3] -> end
 ```
 

examples/xtd.core.examples/hello_worlds/README.md

@@ -3,6 +3,7 @@
 [This folder](.) contains xtd.core "Hello, World!" examples used by [Reference Guide](https://gammasoft71.github.io/xtd/reference_guides/latest/) and more.
 
 * [hello_world_console](hello_world_console/README.md) The classic first application "Hello, World!" with [xtd::console](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1console.html) class.
+* [hello_world_coroutine](hello_world_coroutine/README.md) The classic first application "Hello, World!" with coroutine and [task](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1threading_1_1tasks_1_1task_3_01void_01_4.html).
 * [hello_world_diagnostics](hello_world_diagnostics/README.md) The classic first application "Hello, World!" with [xtd::diagnostics::trace](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1diagnostics_1_1trace.html) class.
 * [hello_world_environment](hello_world_environment/README.md) The classic first application "Hello, World!" with [xtd::environment](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1environment.html) class.
 * [hello_world_io](hello_world_io/README.md) The classic first application "Hello, World!" with [xtd::io::file](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1io_1_1file.html) and [xtd::io::path](https://gammasoft71.github.io/xtd/reference_guides/latest/classxtd_1_1io_1_1path.html) classes.