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