Add a note about botobj.server expected format.
Add a note about botobj.server expected format.

It's a bit confusing otherwise. No code change.

R=tandrii@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1824703002

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py