link to site-repo updated

The Hornet UB is sold at least in the varieties. Without case it is a Hornet UB, with case and without connected USB port it is called AP121. If the USB port is present this device is called AP121U.
We have a AP121U in our mesh http://meshviewer.chemnitz.freifunk.net/#!v:m;n:00c0ca6efffa

This CPE is supported by OpenWRT and already running in Chemnitz

This new feature introduces the new uci section 'gluon-core.wireless' with a preserve_channels option:
 * preserve_channels (boolean)

By setting this option to 1 (true) wifi channels will be preserved during upgrades.

Change the limit to match our recommendation in the site-example.

Fixes #574

fix typo and express sentence regarding update priority clearer

docs: add D-Link DIR-505 (A1) and Buffalo WZR-HP-G300NH (and remove WZR-HP-G300N, it is not actually supported)