Security: Add goals and measures to security.md

[tbongers-cat]

As requested by @klees , this is a proposal for adding security goals and measures to the security.md for documentation.

[corro]

LGTM

[rfalkenstein]

@tbongers-cat would you be so kind and implement the proposed change? Then we can merge this.

[tbongers-cat]

@tbongers-cat would you be so kind and implement the proposed change? Then we can merge this.

Done =)

[rfalkenstein]

Thanks a lot @tbongers-cat