examples: Fix: Add missing description for textonaxes example.

Change-Id: Ibd4053df80e4d1d437688c0d1b2be3612c0b8f5a
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/96
Reviewed-by: Christian Felder <c.felder@fz-juelich.de>
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>