Gtk+: Add a note about ellipsized labels in leaflets

Fixes Librem5/libhandy#63
1 job for <span class="ref-name">leaflet-ellipsized-label</span> in 9 minutes and 35 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #7968
librem5
build_html

00:09:35