doc: api: Add auxdisplay as unstable API

Adds the new auxiliary display peripheral as an unstable API.

Signed-off-by: Jamie McCrae <spam@helper3000.net>
diff --git a/doc/develop/api/overview.rst b/doc/develop/api/overview.rst
index 461e2fc..9eb007f 100644
--- a/doc/develop/api/overview.rst
+++ b/doc/develop/api/overview.rst
@@ -29,6 +29,10 @@
      - Experimental
      - 1.13
 
+   * - :ref:`auxdisplay_api`
+     - Unstable
+     - 3.3
+
    * - :ref:`bluetooth_api`
      - Stable
      - 1.0
diff --git a/doc/hardware/peripherals/index.rst b/doc/hardware/peripherals/index.rst
index 5631556..767b863 100644
--- a/doc/hardware/peripherals/index.rst
+++ b/doc/hardware/peripherals/index.rst
@@ -11,6 +11,7 @@
 
    w1.rst
    adc.rst
+   auxdisplay.rst
    audio/index.rst
    bbram.rst
    bc12.rst