esp-modem(DCE-Factory): Minor corrections per code review

components/esp_modem/docs/internal_docs.rst

@@ -9,6 +9,13 @@ The esp-modem actually implements the DCE class, which in turn aggregates these
 - :ref:`Netif<netif_impl>` to provide the network connectivity
 - :ref:`Module<module_impl>` to define the specific command library
 
+Developers would typically have to
+
+* Add support for a new module
+* Implement a generic (common for all modules) AT command
+
+This is explained in the :ref:`Module<module_impl>` section, as :ref:`Adding new module or command<module_addition>`
+
 ------------
 
 .. doxygengroup:: ESP_MODEM_DCE
@@ -63,6 +70,36 @@ Module abstraction
 .. doxygengroup:: ESP_MODEM_MODULE
    :members:
 
+.. _module_addition:
+
+Adding new devices
+^^^^^^^^^^^^^^^^^^
+
+To support a new module, developers would have to implement a new class derived from :cpp:class:`esp_modem::GenericModule` the same way
+as it is described in the  :ref:`Advanced user manual<create_custom_module>`. The only difference is that the new class (and factory extension)
+would be available in the esp_modem code base.
+
+Implement a new generic command
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Adding a generic command, i.e. the command that is shared for all modules and is included in the :cpp:class:`esp_modem::GenericModule`,
+has to be declared first in the ``include/generate/esp_modem_command_declare.inc`` file, which is the single source
+of supported command definitions, that is used in:
+
+* public C API
+* public CPP API
+* generated documentation
+* implementation of the command
+
+Therefore, a care must be taken, to correctly specify all parameters and types, especially:
+
+* Keep number of parameters low (<= 6, used in preprocessor's forwarding to the command library)
+* Use macros to specify parameter types (as they are used both from C and C++ with different underlying types)
+* Parameter names are used only for clarity and documentation, they get expanded to numbered arguments.
+
+Please use the following pattern: ``INT_IN(p1, baud)``, meaning that the parameter is an input integer,
+human readable argument name is ``baud``, it's the first argument, so expands to ``p1`` (second argument would be ``p2``, etc)
+
 Command library
 ^^^^^^^^^^^^^^^