docs: Add libhandy users

This allows to find in uses examples easily.
3 jobs for hdy-users in 7 minutes and 27 seconds
Status Name Job ID Coverage
  Build
passed build-debian-clang #3174
librem5

00:02:55

passed build-debian-gcc #3173
librem5

00:02:16

25.0%
passed build-debian-package #3175
librem5

00:02:15