added details and link to buy hong kong-located ZTE open phones, to dev_phone page on Marketplace

adding note about flashing your geeksphone to update Firefox OS

fixes made to dev_phone page due to comments from Kevin N and cvan

couple of rogue commas deleted
Merge pull request #1211 from chrisdavidmills/master

added details and link to buy hong kong-located ZTE open phones, to dev_phone page on Marketplace