Threat Model: Roles: Reliances for backend operator

This issue was automatically migrated from github issue https://github.com/TheTorProject/ooni-probe/issues/157.

Hi, @nathan-at-least

I've read through the threat model and it all makes a lot of sense.

When I was reading the Roles section, I expected to see 'Core Developer' as one of the Reliances for 'Backend Operator'. Some of the inter-dependency between these roles is outlined in detail as it relates to MLab and OONI in the Use Cases here under "M-Lab Deployment & Management":

https://github.com/TheTorProject/ooni-probe/wiki/Use-Cases

If you left it out for a specific reason, could you say more? And, if not, I'm happy to add a short note; this is a minor tweak.

Best, Stephen