docs: add information about main(int, char **)

Add information about main(int, argc **) in places where the documentation
stated that only parameterless main could be used

Signed-off-by: Jakub Michalski <jmichalski@internships.antmicro.com>
Signed-off-by: Filip Kokosinski <fkokosinski@antmicro.com>

doc/develop/languages/cpp/index.rst

@@ -31,9 +31,10 @@ or a **cxx** suffix are compiled using the C++ compiler. For example,
 :file:`myCplusplusApp.cpp` is compiled using C++.
 
 The C++ standard requires the ``main()`` function to have the return type of
-``int``. Your ``main()`` must be defined as ``int main(void)``. Zephyr ignores
-the return value from main, so applications should not return status
-information and should, instead, return zero.
+``int``. Your ``main()`` must be defined as ``int main(void)`` or
+``int main(int, char **)``. To use main with arguments the ``CONFIG_BOOTARGS`` option
+has to be selected. Zephyr ignores the return value from main, so applications
+should not return status information and should, instead, return zero.
 
 .. note::
     Do not use C++ for kernel, driver, or system initialization code.

doc/kernel/services/threads/system_threads.rst

@@ -53,11 +53,12 @@ Implementation
 Writing a main() function
 =========================
 
-An application-supplied :c:func:`main` function begins executing once
+An application-supplied ``main()`` function begins executing once
 kernel initialization is complete. The kernel does not pass any arguments
-to the function.
+to the function, unless ``CONFIG_BOOTARGS`` is selected. In such case the
+kernel passes arguments to it and ``main(int, char **)`` can be used.
 
-The following code outlines a trivial :c:func:`main` function.
+The following code outlines a trivial ``main(void)`` function.
 The function used by a real application can be as complex as needed.
 
 .. code-block:: c