Update instructions for multisite

Hi,

I would like to suggest to add a link to

http://codex.gallery2.org/Gallery2:Known_Issues

in the instructions for the update of a multisite (http://codex.gallery2.org/Gallery2:Multisite#How_to_Upgrade_a_Multisite). Its an important piece of information when doing the update on the multisite.

Both documents are also a bit contradictory as the Upgrade guide says that one does not need to run the web upgrader on the core and the Known Issues say it has to be done on the primary site (which I assume is the core)

cheers
martin