talk about the VIRTUALENV and *ARGS options to make..

README.md

@@ -4,3 +4,20 @@ ntunnel
 The ntunnel program is designed to tunnel Unix domain sockets over TCP,
 using the [Noise Protocol](https://noiseprotocol.org/).  The goal is to
 be secure and simple to use and setup.
+
+Running Tests
+-------------
+
+Currently this requires Python 3.x for some of the libraries.  If the
+default virtualenv is not 3.x, you can set the VIRTUALENV variable to
+specify which one to use, such as:
+`make env VIRTUALENV=virtualenv-3.6`
+
+If you want to use an alternate version of python, you can specify
+VIRTUALENVARGS, such as:
+`make env VIRTUALENV=virtualenv-3.6 VIRTUALENVARGS="-p $(which pypy3)"`
+
+Note that I have not tested this w/ pypy3, as when compiling the
+cryptography libraries, it would pick the wrong ones, despite setting
+CFLAGS and LDFLAGS.  It is likely I could make this work, but do not
+know how to.