Add note about pinout in the python 2 debian package, close #862

docs/cli_tools.rst

@@ -36,4 +36,13 @@ The gpiozero package contains a database of information about the various
 revisions of Raspberry Pi. This is queried by the :program:`pinout`
 command-line tool to output details of the GPIO pins available.
 
+.. note::
+
+    Note that only the Python 3 version of the Debian package includes the
+    pinout command line tool, so as not to create a conflict if both versions
+    are installed. If you only installed the ``python-gpiozero`` apt package,
+    the pinout tool will not be available. Instead, you can additionally install
+    the ``python3-gpiozero`` package, or alternatively install gpiozero using
+    pip.
+
 .. include:: cli_pinout.rst