[docs] Nice to have detailed document for new target dynamic

[cuiyanx]

Description

There is not detailed document for new target dynamic. To the user, do not know how to use this target. I find we have added function runJS() through the source code, and we have some others. So I suggest adding an introduction to the document.

Test Code

/src/zjs_modules.c：

zjs_obj_add_function(global_obj, "eval", native_eval_handler);
zjs_obj_add_function(global_obj, "print", native_print_handler);
zjs_obj_add_function(global_obj, "stopJS", stop_js_handler);
zjs_obj_add_function(global_obj, "runJS", zjs_run_js);
zjs_obj_add_function(process, "exit", process_exit);

[brianjjones]

Added with #1876