x/website: wiki doesn't shrink images to fit on the screen

[prattmic]

https://go.dev/wiki/LUCI contains a high-resolution screenshot, which on my screen overflows off the right side of the screen, like below:

IMO, this should be automatically shrunk to fit in the same width as the text.

cc @rsc

[prattmic]

The custom CSS

.Article img {
    width: 100%;
}

Fixes this for me, but I'm not sure that is the best fix. (Will that stretch images that are too small?)

[cagedmantis]

cc @golang/tools-team

[gopherbot]

Change https://go.dev/cl/556416 mentions this issue: _content/css: set img max width to 100%

[hyangah]

In https://go.dev/cl/556416, proposing

max-width: 100%