Merge #11135: Update developer notes with RPC response guidelines

62ecce7 [doc] Add RPC response notes (João Barbosa)

Pull request description:

Tree-SHA512: 795969813eefab47ac03050bd70762fc36d86edb00bdfe1ba76837a810370d61dc88749c51153bd3949eb3885f084b4ba8736b4bbf90dfef65e3fe1939304bd8

doc/developer-notes.md

@@ -619,3 +619,8 @@ A few guidelines for introducing and reviewing new RPC interfaces:
   - *Rationale*: as well as complicating the implementation and interfering
     with the introduction of multi-wallet, wallet and non-wallet code should be
     separated to avoid introducing circular dependencies between code units.
+
+- Try to make the RPC response a JSON object.
+
+  - *Rationale*: If a RPC response is not a JSON object then it is harder to avoid API breakage if
+    new data in the response is needed.