document `super admin` features & permissions

[aleksa-krolls]

Right now, the docs on docs.openfn.org cater to OpenFn SaaS users (as only our team is super admin of the hosted instance).

For users that are deploying OpenFn on their own instance, we should consider where to document features and permissions specific to super admin users (e.g., adding users, modifying platform limits, deployment tips & tricks).

• We should consider where to document features and permissions specific to super admin users (e.g., adding users, modifying platform limits, deployment tips & tricks). Maybe these super admin docs should live on the main repo's README (https://github.com/OpenFn/lightning), but we should align on a decision and make sure we start to actually write down super admin features.
• I'd also like to see an updated user permissions table