os/exec: clarify Cmd.Wait documentation a bit more explicitly
os/exec: clarify Cmd.Wait documentation a bit more explicitly

It already implied that Cmd.Wait is more than os.Process.Wait, but say
so explicitly.

See https://github.com/golang/go/issues/18874#issuecomment-309921486

Updates #18874

Change-Id: Iaa46defd776ae0be817d9f4466a99ac78cfd672b
Reviewed-on: https://go-review.googlesource.com/47650
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

cloudflare/go,golang/go,Cofyc/go,nawawi/go,josharian/go,akutz/go,vsekhar/elastic-go,cloudflare/go,CAFxX/go,cloudflare/go,vsekhar/elastic-go,josharian/go,akutz/go,polyverse-security/go,Cofyc/go,josharian/go,CAFxX/go,nawawi/go,vsekhar/elastic-go,polyverse-security/go,polyverse-security/go,codestation/go,nawawi/go,codestation/go,akutz/go,CAFxX/go,vsekhar/elastic-go,josharian/go,Cofyc/go,golang/go,Cofyc/go,cloudflare/go,polyverse-security/go,akutz/go,cloudflare/go,nawawi/go,polyverse-security/go,CAFxX/go,golang/go,vsekhar/elastic-go,nawawi/go,Cofyc/go,codestation/go,akutz/go,nawawi/go,Cofyc/go,golang/go,akutz/go,golang/go,codestation/go,vsekhar/elastic-go,cloudflare/go,codestation/go,cloudflare/go,nawawi/go,christopher-henderson/Go,vsekhar/elastic-go,josharian/go,polyverse-security/go,Cofyc/go,akutz/go,josharian/go,CAFxX/go,codestation/go,golang/go,nawawi/go,CAFxX/go,Cofyc/go,cloudflare/go,akutz/go,golang/go,polyverse-security/go,josharian/go,golang/go,codestation/go,CAFxX/go,josharian/go,vsekhar/elastic-go,polyverse-security/go,CAFxX/go,codestation/go