doc: fix link in contribute.html
doc: fix link in contribute.html

Fixes #26611

Change-Id: I111152c7b1156a461c9ddeaf16d2fe7a2d5a00c1
GitHub-Last-Rev: 72090d539b5601b8c585628a11a99b03103d5a75
GitHub-Pull-Request: golang/go#26724
Reviewed-on: https://go-review.googlesource.com/126935
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

josharian/go,CAFxX/go,nawawi/go,josharian/go,josharian/go,CAFxX/go,cloudflare/go,CAFxX/go,cloudflare/go,akutz/go,akutz/go,akutz/go,akutz/go,golang/go,golang/go,CAFxX/go,josharian/go,golang/go,golang/go,nawawi/go,nawawi/go,nawawi/go,josharian/go,CAFxX/go,cloudflare/go,golang/go,akutz/go,golang/go,josharian/go,nawawi/go,nawawi/go,cloudflare/go,cloudflare/go,CAFxX/go,golang/go,josharian/go,CAFxX/go,cloudflare/go,akutz/go,josharian/go,nawawi/go,cloudflare/go,akutz/go,golang/go,akutz/go,cloudflare/go,nawawi/go,CAFxX/go