ADB: Add URL at end of --help

Test: NA
Bug: NA
Change-Id: I0ee68be4373683691b8c82c243d3337a5b8e5763
diff --git a/client/commandline.cpp b/client/commandline.cpp
index a0e3521..dfe1594 100644
--- a/client/commandline.cpp
+++ b/client/commandline.cpp
@@ -252,6 +252,9 @@
         " $ANDROID_LOG_TAGS        tags to be used by logcat (see logcat --help)\n"
         " $ADB_LOCAL_TRANSPORT_MAX_PORT max emulator scan port (default 5585, 16 emus)\n"
         " $ADB_MDNS_AUTO_CONNECT   comma-separated list of mdns services to allow auto-connect (default adb-tls-connect)\n"
+        "\n"
+        "Online documentation: https://android.googlesource.com/platform/packages/modules/adb/+/refs/heads/master/docs/user/adb.1.md\n"
+        "\n"
     );
     // clang-format on
 }