add prerequisites info and ways to run the testsuite

README.rst

@@ -50,6 +50,27 @@ The library currently contains functions to:
 - play a playlist (parsed MML) using PWM on GPIO pins on ESP boards
   under MicroPython (experimental; may not work for higher pitches)
 
+Prerequisites
+-------------
+
+The library itself does not have any prerequisites, but ``argparse``
+is used by the (optional) command-line interface.
+
+While MMLlib is only formally supported for Python releases that
+are not end-of-life it’s occasionally tested that Python 2.7 and
+even 2.5 still work, with no guarantees though.
+
+Testsuite
+---------
+
+The testsuite can be run with one of the following commands:
+
+-  ``python3 setup.py test`` (3.x) or ``python setup.py test`` (2.5+)
+   (note that this is deprecated in recent versions of setuptools;
+   use one of the other methods if it fails)
+-  ``python3 -m unittest`` (3.x)
+-  ``python -m unittest discover`` (2.7+)
+
 Examples
 --------