meta: add issue template for API reference docs

Prior to this commit, there was no GitHub issue template guiding
users to open issues about gaps in the API reference docs.

Refs: https://github.com/nodejs/node/pull/31123
PR-URL: https://github.com/nodejs/node/pull/32944
Fixes: https://github.com/nodejs/nodejs.org/issues/2866


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>