Bug#801359: mention "adb help" on the adb man page

[積丹尼 Dan Jacobson]

Package: android-tools-adb
Version: 4.2.2+git20130529-5.1
Severity: wishlist
File: /usr/share/man/man1/adb.1.gz

$ adb help
also works good. Mention it there on the man page, as not everybody
might be connected to the Internet.