Update our "Chocolatey takes security very seriously" / Security page

### What You Are Seeing?

Formatting here is inconsistent and I think emphasis in this article is over-done, leading to a fairly defensive and salty (for lack of a better word) tone, at least to my eye.

Some of the copy here needs a good do-over. Crossed-out portions perhaps could be moved to their own "Done" or "Resolved" sections.

### What is Expected?

- The initial framing of this document feels like it's intended to be informational. Some portions feel more argumentative than informational, and I think we can arrange this information in a more clear manner.
- Overuse of strikethroughs makes some of this a bit difficult to read as well.
- General use of text-emphasis formatting can be reduced, I think it just reads too defensive to be constantly emphasising `Chocolatey **USED** to be insecure`. If it was, it was, nbd, it's fixed now.
- The public key tokens in the copy and the example for `sn.exe` just below it should (probably?) agree with each other.
- Overall I think this article could benefit from a much more neutral and matter-of-fact tone than it currently has.
- TLDR header / preamble at the top isn't really adding anything.

Start with the Security page and review its formatting, strikethroughs, emphasis, public-key tokens, sn.exe example, and TLDR preamble. Done means the page has a clearer, neutral, informational structure with consistent examples and less unnecessary emphasis.

Written by the indexing model from the issue text.