Stop treating a single shared chat as a misconfiguration

Reporting to BASECAMP_CHATBOT_URL is a working setup — the second variable
exists only for those who want release traffic in its own chat. setup now
states which chat receives reports instead of warning about the common case,
and the README frames the split as optional rather than expected.

bin/setup

@@ -280,9 +280,11 @@ if [[ -f "$CREDENTIALS" ]]; then
   if grep -q 'OMARCHY_RELEASE_CHATBOT_URL' "$CREDENTIALS"; then
     print_success "Release reports go to the dedicated release chat"
   elif grep -q 'BASECAMP_CHATBOT_URL' "$CREDENTIALS"; then
-    print_warning "Release reports fall back to BASECAMP_CHATBOT_URL (the repository chat)"
-    echo "    Export OMARCHY_RELEASE_CHATBOT_URL in $CREDENTIALS to send them"
-    echo "    to their own chat instead."
+    # A working setup, not a problem: one chat receives everything. Splitting
+    # them is a preference, so this states the fact rather than nagging.
+    print_success "Release reports go to BASECAMP_CHATBOT_URL (shared with the sync workflows)"
+    echo "    To give releases their own Basecamp chat, create one, add a chatbot"
+    echo "    to it, and export its lines URL as OMARCHY_RELEASE_CHATBOT_URL here."
   else
     print_warning "No chatbot URL in $CREDENTIALS — build reports are disabled"
     echo "    Export OMARCHY_RELEASE_CHATBOT_URL to receive start/publish/failure"