Help page redesign

[Sakib25800]

Redesigns the help page and adds some base styling.

• Fira Sans is used since other Rust sites use it
• Fira Mono for code blocks
• #28607F is official Rust blue

[Kobzol]

Oh wow, I had no idea we even have such design constraints 😆 Where did you find out about the blue? :D

Could you please make the content max width be a bit wider? It's quite narrow on my FullHD monitor, kind of unnecessarily. Otherwise the page looks beautiful.

[Sakib25800]

• Rust Blue
• Increased width from 50rem -> 80rem.

Technically that's the Rust Foundation brand colors, but it's official enough for me.

[Kobzol]

Thanks! I went through the commands on the help page and noticed that it doesn't fully correspond to the help command (e.g. delegate=try is missing). Could you please double check it and make sure that everything that is in @bors help is on the help page? Thanks!

[Sakib25800]

I've made sure that the help command and help page now match and also added rollup and rollup- to the help command as it was missing.

[Kobzol]

Thanks! Reading the help table in HTML is quite difficult, eventually we should define the help commands in Rust (even with just a tuple of (cmd, permissions, description) and then just render it in the template with a for loop, to avoid repeating all the HTML table items. But that doesn't need to happen here.