[doc] developer-notes.md: point out that UniValue deviates from upstream

Author: Sjors

doc/developer-notes.md

@@ -714,7 +714,7 @@ Current subtrees include:
   - Upstream at https://github.com/bitcoin-core/ctaes ; actively maintained by Core contributors.
 
 - src/univalue
-  - Upstream at https://github.com/jgarzik/univalue ; report important PRs to Core to avoid delay.
+  - Upstream at https://github.com/bitcoin-core/univalue ; actively maintained by Core contributors, deviates from upstream https://github.com/jgarzik/univalue
 
 Upgrading LevelDB
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