proxy.golang.org: mention retract directive in documentation

[seankhliao]

From the FAQ:

I removed a bad release from my repository but it still appears in the mirror, what should I do?

Whenever possible, the mirror aims to cache content in order to avoid breaking builds for people that depend on your package, so this bad release may still be available in the mirror even if it is not available at the origin. The same situation applies if you delete your entire repository. We suggest creating a new version and encouraging people to use that one instead.

The go.mod retract directive should also be mentioned/linked

[mknyszek]

CC @katiehockman @heschi @hyangah

[katiehockman]

@mknyszek This issue is about the documentation at proxy.golang.org, not pkg.go.dev, so I went ahead and reverted the title change. LMK if I'm missing something.

[mknyszek]

Ah, my apologies. I asked who to CC here and I was directed to you. Do you know who the right owner is for proxy.golang.org?

[katiehockman]

You have the right owners (including me)! I was just noting that the title of the issue was correct as it was originally filed (ie. for proxy.golang.org), and shouldn't have been changed to pkg.go.dev, which is why I put it back. No worries :)

We'll take a look at updating our documentation for the site, so thanks for CCing us.

[jamalc]

The retract directive documentation has been added proxy.golang.org FAQ.