doc/go1.16: reference misc/ios/README for how to build iOS programs
doc/go1.16: reference misc/ios/README for how to build iOS programs

Updates #43371, #43343.

Change-Id: Ib89b809a5220717507272453ea86224d1928dd36
Reviewed-on: https://go-review.googlesource.com/c/go/+/280154
Trust: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

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