printf analyzer: link to fmt#Printing for verb/type docs
printf analyzer: link to fmt#Printing for verb/type docs

Folks are reporting the current error message as not useful,
remarking that they don’t know which formatting verb goes with
which Go type, see e.g. b/227741360.

Change-Id: I367bc8c4df3521f0726dc4defa4e563532706148
Reviewed-on: https://go-review.googlesource.com/c/tools/+/422854
Reviewed-by: Nicolas Hillegeer <178184bf77e7c5ae86300dd7107a89212029c9e8@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>
Run-TryBot: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>
gopls-CI: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools