download: Document "First steps"

That is, default username/password, a mention about that we don't ship
plugins, and service names.

Signed-off-by: Robin Sonefors <ozamosi@flukkost.nu>
download: Put icons for both core and suite

Instead of having an icon for core, and a link to suite.

Signed-off-by: Robin Sonefors <ozamosi@flukkost.nu>