Create funding.json (libp2p#5553)

## Description

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funding.json

@@ -0,0 +1,5 @@
+{
+  "opRetro": {
+    "projectId": "0x966804cb492e1a4bde5d781a676a44a23d69aa5dd2562fa7a4f95bb606021c8b"
+  }
+}