docs: reword secureblue's goal to 'maximize Linux security'

[Ganwtrs]

the security architecture of desktop Linux is broadly and significantly lacking. The goal of secureblue is to build a maximally secure Linux operating system

secureblue's goal is to make Linux security as best as it can be, but that wouldn't necessarily mean Linux would be reasonably secure

[RoyalOughtness]

Our mission is to make desktop linux secure, that doesn't mean we've achieved it. This is stated on the same page

[Ganwtrs]

Our mission is to make desktop linux secure, that doesn't mean we've achieved it. This is stated on the same page

The goal of secureblue is to build a maximally secure Linux operating system
we aim for instead is to be the most secure option for those who already intend to use Linux

Maximally secure for Linux and being the most secure option for Linux doesn't necessarily mean secure in general though, that's why I made this PR assuming the goal was just maximally secure desktop Linux. If you want the about page of the website to adhere more to the goal you've explained in this discussion (making Linux secure), I would be happy to help with that

Being maximally secure for Linux is also more realistic than making Linux secure, but I admire this goal either way!