.github: add link to questions in ISSUE_TEMPLATE
.github: add link to questions in ISSUE_TEMPLATE

Add a link redirecting questions to the wiki page/forums

Change-Id: I05b784e6bb0c260cb01c4535ad05fb17ba80110e
GitHub-Last-Rev: a927ce5c69df7854ae919013b0e55ab4d356fc4c
GitHub-Pull-Request: golang/go#36413
Reviewed-on: https://go-review.googlesource.com/c/go/+/213440
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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