Add terse documentation for pinout tool

Author: stewartadcock

docs/cli_pinout.rst

@@ -0,0 +1,26 @@
+==================
+Command-line Tools
+==================
+
+Pinout
+======
+
+The gpiozero package contains a database of information about the various
+revisions of Raspberry Pi. This is queried by the ``pinout`` command-line
+tool to write details of the GPIO pins available.
+
+Unless specified, the revision of the current device will be detected. A
+particular revision may be selected with the --revision command-line
+option. *e.g.*:
+
+    pinout.py --revision 000d
+
+By default, the output will include ANSI color codes if run in a color-capable
+terminal. This behaviour may be overridden by the --color or --monochrome
+options to force colored or non-colored output, respectively. *e.g.*:
+
+    pinout.py --monochrome
+
+Full usage details are available with:
+
+    pinout.py --help

docs/index.rst

@@ -18,6 +18,7 @@ Table of Contents
     api_tools
     api_pins
     api_exc
+    cli_pinout
     changelog
     license