doc: Update documentation

Signed-off-by: Rahix <rahix@rahix.de>

Documentation/epicardium/intro.rst

 Epicardium Intro
 ================
-
 Epicardium is the main component of the firmware.  It runs on core0 and is
 based on FreeRTOS.  Epicardium provides an API to a payload running on the
 other core which exposes most functionality.
 
+API Design
+----------
+.. note::
+
+   This is the current design.  We might adjust it in the future to allow for
+   more performance in cases where this approach is too slow.
+
+The API is strictly synchroneous.  This means, an API call looks exactly the
+same as calling any other function.  Internally, the call will wake up
+Epicardium and dispatch the call.  Once the call has finished, it will return a
+result.
+
+
+API Conventions
+---------------
 The API functions follow the kernel convention of either returning a boolean if
 the function is a predicate or returning a success integer (with negative
 values denoting errors) if it is an action or imperative command.  To quote:

Documentation/pycardium/intro.rst

 Pycardium Intro
 ===============
-
 Pycardium is a core1 payload based on MicroPython.  It can interface with
 card10 using the Epicardium API, which is wrapped in a bunch of python modules.
+Pycardium also contains a number of Python stdlib modules.  To see the full
+list, type:
+
+.. code-block:: python
+
+   help("modules")
+
+
+The following pages detail card10 specific modules.