update README

Author: smurfix

README.rst

@@ -1,10 +1,19 @@
 asyncgpio
 =========
 
-Trio-GPIO allows easy access to the GPIO pins on your Raspberry Pi or
+AsyncGPIO allows easy access to the GPIO pins on your Raspberry Pi or
 similar embedded computer.
 
 It is based on libgpiod and its CFFI adapter by Steven P. Goldsmith
 <[email protected]>, as downloaded from
 `github <https://github.com/sgjava/userspaceio.git>`_.
 
+Testing AsyncGPIO requires a Linux distribution that enables the mock-GPIO module.
+As of mid-2020, Debian's kernel does not include this module, but Raspbian's does.
+
+If you can compile your own kernel: the option is named CONFIG_GPIO_MOCKUP,
+in Device Drivers / GPIO support / Memory mapped GPIO drivers / GPIO
+Testing Driver.
+
+Writing an actual test suite is TODO. There is a more elaborate test script
+in `DistKV-GPIO <https://github.com/smurfix/distgpio>`_.