Handling of MIME types

Hi there,
I have successfully created a .desktop file for my snapped application (brynhild) and it shows up correctly in the start menu etc:

apps:
brynhild:
command: bin/desktop-launch $SNAP/brynhild
desktop: desktop/volsung-brynhild.desktop

This is how the desktop file looks like:
[Desktop Entry]
Encoding=UTF-8
Version=1.0
Type=Application
Terminal=false
Exec=brynhild %F
Name=Brynhild
Icon=brynhild-icon
Categories=Geothermal;
MimeType=application/x-brynhild;

Question: There is currently no reference to the file brynhild.xml which defines my MimeType in the snapcraft.yaml file. How would I reference it correctly so that the snapped volsung.brynhild application associates with it?