doc/go1.16: add text/template changes to release notes
doc/go1.16: add text/template changes to release notes

For #40700
Fixes #42914

Change-Id: I673d86a946c362e28bfbf35fab2c60ebfbd8bda2
Reviewed-on: https://go-review.googlesource.com/c/go/+/274472
Trust: Alberto Donizetti <90b16103a35511ced020676f3544f17117fb4c92@gmail.com>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

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