Update documentation to add SQLAgentReaderRole as a requirement for minimal permissions

[DavidWiseman]

Discussed in #176

^{Originally posted by BrubiSQL April 28, 2022}
Suggestion for edit of this doc: https://github.com/trimble-oss/dba-dash/blob/main/Docs/Security.md

To allow DBA Dash to read Jobs, and stuff relating to it, you need to add

USE [msdb]
GO
ALTER ROLE [SQLAgentReaderRole] ADD MEMBER [DBAdashUser]
GO
```</div>

[DavidWiseman]

Docs updated