Documented adb install --instant

Test: m -j32 adb && ./out/host/linux-x86/bin/adb help 2>&1 | grep instant
Bug: 79422318

Change-Id: I2830a9e3cf81becac1a6334670d8dc487fe72322
diff --git a/adb/client/commandline.cpp b/adb/client/commandline.cpp
index e476e07..39983ab 100644
--- a/adb/client/commandline.cpp
+++ b/adb/client/commandline.cpp
@@ -149,8 +149,8 @@
         " emu COMMAND              run emulator console command\n"
         "\n"
         "app installation:\n"
-        " install [-lrtsdg] PACKAGE\n"
-        " install-multiple [-lrtsdpg] PACKAGE...\n"
+        " install [-lrtsdg] [--instant] PACKAGE\n"
+        " install-multiple [-lrtsdpg] [--instant] PACKAGE...\n"
         "     push package(s) to the device and install them\n"
         "     -l: forward lock application\n"
         "     -r: replace existing application\n"
@@ -159,6 +159,7 @@
         "     -d: allow version code downgrade (debuggable packages only)\n"
         "     -p: partial application install (install-multiple only)\n"
         "     -g: grant all runtime permissions\n"
+        "     --instant: cause the app to be installed as an ephemeral install app\n"
         " uninstall [-k] PACKAGE\n"
         "     remove this app package from the device\n"
         "     '-k': keep the data and cache directories\n"