misc/ios: document the external binary and the required env variables

Change-Id: I1ec2460758b19e5315be061033c1bb5ed9ead4a8
Reviewed-on: https://go-review.googlesource.com/9688Reviewed-by: Minux Ma <minux@golang.org>

misc/ios/detect.go

@@ -7,6 +7,9 @@
 // detect attempts to autodetect the correct
 // values of the environment variables
 // used by go_darwin_arm_exec.
+// detect shells out to ideviceinfo, a third party program that can
+// be obtained by following the instructions at
+// https://github.com/libimobiledevice/libimobiledevice.
 package main
 
 import (

misc/ios/go_darwin_arm_exec.go

@@ -59,8 +59,15 @@ func main() {
 		log.Fatal("usage: go_darwin_arm_exec a.out")
 	}
 
+	// e.g. B393DDEB490947F5A463FD074299B6C0AXXXXXXX
 	devID = getenv("GOIOS_DEV_ID")
+
+	// e.g. Z8B3JBXXXX.org.golang.sample, Z8B3JBXXXX prefix is available at
+	// https://developer.apple.com/membercenter/index.action#accountSummary as Team ID.
 	appID = getenv("GOIOS_APP_ID")
+
+	// e.g. Z8B3JBXXXX, available at
+	// https://developer.apple.com/membercenter/index.action#accountSummary as Team ID.
 	teamID = getenv("GOIOS_TEAM_ID")
 
 	var err error