doc: hardware: peripheral: Add auxdisplay documentation

Adds base auxdisplay documentation.

Signed-off-by: Jamie McCrae <spam@helper3000.net>

doc/hardware/peripherals/auxdisplay.rst

@@ -0,0 +1,30 @@
+.. _auxdisplay_api:
+
+Auxiliary Display (auxdisplay)
+##############################
+
+Overview
+********
+
+Auxiliary Displays are text-based displays that have simple interfaces for
+displaying textual, numeric or alphanumeric data, as opposed to the
+`Display API <display_api>`_, auxiliary displays do not support custom
+graphical output to displays (and and most often monochrome), the most
+advanced custom feature supported is generation of custom characters.
+These inexpensive displays are commonly found with various configurations
+and sizes, a common display size is 16 characters by 2 lines.
+
+This API is unstable and subject to change.
+
+Configuration Options
+*********************
+
+Related configuration options:
+
+* :kconfig:option:`CONFIG_AUXDISPLAY`
+* :kconfig:option:`CONFIG_AUXDISPLAY_INIT_PRIORITY`
+
+API Reference
+*************
+
+.. doxygengroup:: auxdisplay_interface