document address, crypto, and util

src/util/bytes_mobile.go

@@ -8,12 +8,14 @@ func init() {
 	debug.SetGCPercent(25)
 }
 
-// On mobile, just return a nil slice.
+// GetBytes always returns a nil slice on mobile platforms.
 func GetBytes() []byte {
 	return nil
 }
 
-// On mobile, don't do anything.
+// PutBytes does literally nothing on mobile platforms.
+// This is done rather than keeping a free list of bytes on platforms with memory constraints.
+// It's needed to help keep memory usage low enough to fall under the limits set for e.g. iOS NEPacketTunnelProvider apps.
 func PutBytes(bs []byte) {
 	return
 }