doc/go1.16: document net.ErrClosed usage in crypto/tls
doc/go1.16: document net.ErrClosed usage in crypto/tls

Change-Id: I130cf79b93c6456dbe87f0042209e204c4e319b2
Reviewed-on: https://go-review.googlesource.com/c/go/+/257457
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>
Trust: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>

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