docs: Added "Verifying for ART" to TOC.

Now that "Verifying App Behavior on the Android Runtime (ART)"
(guide/practices/verifying-apps-art.jd) is published, also adding it
to the "API Guides" TOC.

You can verify it at

http://asolovay.mtv:9001/guide/practices/index.html

(...it's the last element in the "Best Practices" submenu.)

Change-Id: If7b445616768d17193309dbd3075b2630652ac96