add artifacts to release

.github/workflows/build.yml

@@ -48,3 +48,10 @@ jobs:
         name: elf files
         path: build/*.elf
 
+    - name: Create release
+      if: startsWith(github.ref, 'refs/tags/')
+      uses: softprops/action-gh-release@v1
+      with:
+        files: build*/*.uf2
+        fail_on_unmatched_files: true
+        body: "Select a uf2 from the list below."