adb: add `--abi` to the `adb install` help.

A bit of a break with convention, but we do already document `-t` which
is actually a PackageManager option, not an adb option, and `--abi`
seems like it'll be seeing increased usage these next few years.

Also add a pointer to `adb shell pm help` for full details of
PackageManager options.

Bug: http://b/122487331
Test: manual
Change-Id: I93f48d202e5707b27caadb5af2a65c485c6d3407

adb/client/commandline.cpp

@@ -153,6 +153,7 @@ static void help() {
         "     -d: allow version code downgrade (debuggable packages only)\n"
         "     -p: partial application install (install-multiple only)\n"
         "     -g: grant all runtime permissions\n"
+        "     --abi ABI: override platform's default ABI\n"
         "     --instant: cause the app to be installed as an ephemeral install app\n"
         "     --no-streaming: always push APK to device and invoke Package Manager as separate steps\n"
         "     --streaming: force streaming APK directly into Package Manager\n"
@@ -164,6 +165,7 @@ static void help() {
 #ifndef _WIN32
         "     --local-agent: locate agent files from local source build (instead of SDK location)\n"
 #endif
+        "     (See also `adb shell pm help` for more options.)\n"
         //TODO--installlog <filename>
         " uninstall [-k] PACKAGE\n"
         "     remove this app package from the device\n"