docs: Limit the max-width of paragraphs for readability

[dfabulich]

There's no max-width on the paragraphs of the Skip documentation, so the lines go as wide as the monitor will allow.

I wrote a little CSS override to set p { max-width: 60ch; } and it's much more readable.

https://ux.stackexchange.com/a/108803/2222

Before

After