Edits content to add clarity and consistent tone

@Lukasa Here are a few suggested updates to the "about" page. There was one behavior change for the `certifi` link. The link was going to an unknown destination. I think that it now links to the correct site.

The title "Security Considerations" didn't feel quite right to me so I shortened to "Security" mainly because I couldn't think of a more concrete, stronger word than "Considerations".

The rest of the changes are just for clarity, tone, or style.