README: fix hackathon tags to namespaced format

README.md

@@ -10,11 +10,13 @@ app_file: app.py
 pinned: false
 license: apache-2.0
 tags:
-  - backyard-ai
-  - well-tuned
-  - off-brand
-  - sharing-is-caring
-  - field-notes
+  - build-small-hackathon
+  - track:backyard
+  - achievement:welltuned
+  - achievement:offbrand
+  - achievement:sharing
+  - sponsor:openbmb
+  - sponsor:modal
 ---
 
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