doc: add example for conversion from slice expressions to array ptr
doc: add example for conversion from slice expressions to array ptr

Fixes #47599

Change-Id: I8f4ccd3b0c2bcdb057ee853163b4421229141333
Reviewed-on: https://go-review.googlesource.com/c/go/+/340351
Trust: Cuong Manh Le <54b4457f1dff6823379654eb5867596497ba782f@gmail.com>
Run-TryBot: Cuong Manh Le <54b4457f1dff6823379654eb5867596497ba782f@gmail.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

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