docs/system: Briefly document canon-a1100 board

Add skeletal documentation of the canon-a1100 board.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20200713175746.5936-2-peter.maydell@linaro.org

docs/system/arm/digic.rst

@@ -0,0 +1,11 @@
+Canon A1100 (``canon-a1100``)
+=============================
+
+This machine is a model of the Canon PowerShot A1100 camera, which
+uses the DIGIC SoC. This model is based on reverse engineering efforts
+by the contributors to the `CHDK <http://chdk.wikia.com/>`_ and
+`Magic Lantern <http://www.magiclantern.fm/>`_ projects.
+
+The emulation is incomplete. In particular it can't be used
+to run the original camera firmware, but it can successfully run
+an experimental version of the `barebox bootloader <http://www.barebox.org/>`_.

docs/system/target-arm.rst

@@ -82,6 +82,7 @@ undocumented; you can get a complete list by running
    arm/versatile
    arm/vexpress
    arm/aspeed
+   arm/digic
    arm/musicpal
    arm/nseries
    arm/orangepi