ADB: Document ConnectionState

Provide meaning for all "states" in the enum.

Test: NA
Bug: NA
Change-Id: Ic2828a893aa74673e2d11db7ee09d4bb681b4e5e
diff --git a/adb.h b/adb.h
index 39bdedb..43cd6ff 100644
--- a/adb.h
+++ b/adb.h
@@ -111,12 +111,14 @@
     kCsDetached,        // USB device that's detached from the adb server.
     kCsOffline,
 
-    kCsBootloader,
-    kCsDevice,
-    kCsHost,
-    kCsRecovery,
-    kCsSideload,
-    kCsRescue,
+    // After CNXN packet, the ConnectionState describes not a state but the type of service
+    // on the other end of the transport.
+    kCsBootloader,  // Device running fastboot OS (fastboot) or userspace fastboot (fastbootd).
+    kCsDevice,      // Device running Android OS (adbd).
+    kCsHost,        // What a device sees from its end of a Transport (adb host).
+    kCsRecovery,    // Device with bootloader loaded but no ROM OS loaded (adbd).
+    kCsSideload,    // Device running Android OS Sideload mode (minadbd sideload mode).
+    kCsRescue,      // Device running Android OS Rescue mode (minadbd rescue mode).
 };
 
 std::string to_string(ConnectionState state);