give every network option its own exposition, not just offscale

Each of the three now carries a couple of lines under it, separated by a blank
line, so the choice can be made from the menu itself rather than by typing ? and
reading a page. 2 and 3 are written; offscale's is a marked placeholder with your
one-liner standing in until the longer copy arrives.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/setup/machine-setup/lib/tailscale.sh

@@ -61,10 +61,21 @@ tailscale_help() {
 tailscale_network_menu() {
   info "Which network should this machine join?"
   echo ""
-  echo "     [1] set up your own network        (offscale)"
-  echo "         offscale is just tailscale and headscale, with our own sugar on top"
-  echo "     [2] use a network you already run  (headscale, offscale)"
-  echo "     [3] the easy route                 (tailscale.com)"
+  echo "     [1] set up your own network — offscale"
+  # TODO(pastilhas): your copy. Enough that somebody who has never heard the name
+  # knows what they are choosing, without having to type ?.
+  echo "         offscale is just tailscale and headscale, with our own sugar on top."
+  echo "         [ to be written ]"
+  echo ""
+  echo "     [2] use a network you already run — headscale or offscale"
+  echo "         You already have a coordination server somewhere. Point this"
+  echo "         machine at it and it joins that network alongside the rest."
+  echo ""
+  echo "     [3] the easy route — tailscale.com"
+  echo "         Tailscale runs the coordination for you. Nothing to host and"
+  echo "         nothing to maintain, free for personal use; the trade is that"
+  echo "         the list of your machines lives with them."
+  echo ""
   echo "     [?] what are tailscale, headscale and offscale?"
   echo ""
 }