fmt: document verbs %b %d %o %x %X for printing pointers
fmt: document verbs %b %d %o %x %X for printing pointers

This has been supported since Go 1 and there's even a test for it.
The documentation was missing.

Fixes #21409.

Change-Id: I5813488f6a98c1b4506c239e968d43344b91be12
Reviewed-on: https://go-review.googlesource.com/59412
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

cloudflare/go,polyverse-security/go,CAFxX/go,CAFxX/go,CAFxX/go,golang/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,Cofyc/go,Cofyc/go,josharian/go,josharian/go,nawawi/go,nawawi/go,cloudflare/go,nawawi/go,golang/go,polyverse-security/go,golang/go,josharian/go,cloudflare/go,josharian/go,polyverse-security/go,cloudflare/go,polyverse-security/go,nawawi/go,akutz/go,Cofyc/go,CAFxX/go,CAFxX/go,golang/go,polyverse-security/go,codestation/go,codestation/go,akutz/go,codestation/go,akutz/go,codestation/go,josharian/go,codestation/go,CAFxX/go,Cofyc/go,josharian/go,golang/go,CAFxX/go,polyverse-security/go,cloudflare/go,akutz/go,cloudflare/go,akutz/go,josharian/go,akutz/go,Cofyc/go,Cofyc/go,akutz/go,akutz/go,codestation/go,polyverse-security/go,cloudflare/go,Cofyc/go,Cofyc/go,codestation/go,polyverse-security/go,codestation/go,golang/go,nawawi/go,nawawi/go,nawawi/go,golang/go,christopher-henderson/Go,josharian/go