Currently the manual doesn't clearly say whether `homectl update username -G group` will append the group to the user, or overwrite the list and remove user from the groups that aren't specified.
Fix this by updating the manual, basing the change on the usermod manual.
8db8f99eb9 man: add note regarding editing user groups
man/homectl.xml | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)