doc/articles/wiki: highlight the use of _ warning
doc/articles/wiki: highlight the use of _ warning

This moves the paragraph mentioning the use of _ higher up
to emphasize the warning and thereby reducing chances of getting
stuck.

Fixes #22617

Change-Id: I64352a3e966a22d86fc9d381332bade49d74714a
Reviewed-on: https://go-review.googlesource.com/87375
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

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