better explain scoring maturity levels

[SebaDele]

From Rainer Haffman in Slack - https://owasp.slack.com/archives/C0VF1EJGH/p1652302629341629
At the beginning, when I started with SAMM, I couldn't understand how the points are given in SAMM. I then found out with the help of the toolbox. Personally, I think it would be a good idea for newcomers to document this on the website. I think a good place for this would be on the "Assessment" page. Additionally, it could be addressed in the FAQ