[Security Insights] Clarify what roles and permissions enable

### Existing documentation URL(s)

- https://developers.cloudflare.com/security-center/security-insights/roles-and-permissions/

### What changes are you suggesting?

Background
- Account administrator got an email notification about security threats detection
- Account administrator granted me `Administrator Read Only` role on the account as mentioned by the documentation linked above

Result
- Correct behaviour: I have access to Security Insights page in the menu
- **Unexpected behaviour**
- Overview is empty
- Can't see any insight
- Can't run security scan

My guess is I need the `Administrator` role, or I'm missing other permissions, but documentation is unclear about this. Please update the documentation to clarify what actions are available for each role.

### Additional information

Configured role

Security Insights page