spec: add section on instantiation
spec: add section on instantiation

Change-Id: I2770da87b4c977b51dfa046f2f08283917675e1c
Reviewed-on: https://go-review.googlesource.com/c/go/+/365916
Trust: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
Trust: Dan Scales <7338a4f274e3bf1354488b9d1f344f4c9a69a8fb@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Dan Scales <7338a4f274e3bf1354488b9d1f344f4c9a69a8fb@google.com>

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