crypto/rand: make documentation consistent between package comment and Reader
crypto/rand: make documentation consistent between package comment and Reader

Updates #25959

Change-Id: I9ae64b216ab5807718db0db98b32de1dc5fa4bec
Reviewed-on: https://go-review.googlesource.com/119875
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>
Reviewed-by: Filippo Valsorda <4f40cda291c5f9634e1affd3db44947af61f705c@golang.org>

cloudflare/go,nawawi/go,golang/go,golang/go,akutz/go,CAFxX/go,CAFxX/go,josharian/go,CAFxX/go,nawawi/go,josharian/go,akutz/go,cloudflare/go,josharian/go,CAFxX/go,josharian/go,CAFxX/go,golang/go,akutz/go,akutz/go,nawawi/go,nawawi/go,CAFxX/go,golang/go,josharian/go,akutz/go,CAFxX/go,cloudflare/go,golang/go,CAFxX/go,cloudflare/go,cloudflare/go,akutz/go,golang/go,josharian/go,nawawi/go,cloudflare/go,nawawi/go,cloudflare/go,nawawi/go,golang/go,golang/go,nawawi/go,cloudflare/go,josharian/go,josharian/go,akutz/go,akutz/go