Add example of accessing beamline via group admin

[tpoliaw]

Not sure if this is the best approach but from looking at the data from the
bundler, some beamlines are grouped rather than having their own admin roles,
eg, i22_admin and b21_admin are not present but saxs_admin is. Presumably
em_admin and the microscopes etc are the same.

Would it be possible to include a admin_permissions list in the beamlines data
section of the bundler data to prevent all these rules having to be hardcoded?

[tpoliaw]

Looks like my guess at contains syntax doesn't work but you get the idea