readme: use the repo description as the tagline

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -1,5 +1,8 @@
 # Coopertron 5000
 
+Using AI to synthesize viewpoints to build consensus while highlighting novel
+ideas or dissent.
+
 A benevolent robot that reads the co-op's anonymous pre-meeting braindump and
 tells the members what they said. Built for Inference Cooperative meetings.
 Members answer a short form before a meeting (ideas, wants, needs, goals,