docs: add details about constraints API (#897)

Author: mikhailUshakoff

permissionless/README.md

@@ -28,4 +28,16 @@ The permissionless implementation has been suspended. The latest implementation
                 // }
     ```
 - devnet, added usage for permissionless-driver
-  - branch: https://github.com/NethermindEth/simple-taiko-node-nethermind/tree/catalyst_pacaya_shasta-urc
+  - branch: https://github.com/NethermindEth/simple-taiko-node-nethermind/tree/catalyst_pacaya_shasta-urc
+
+## Constraints API
+
+We were exploring the use of https://github.com/eth-fabric/fabric/commit/11052eb5941a0ae21dd30c161c4146e51a38c1a1 to enable forced inclusion into L1 blocks.
+
+During testing, we identified a potential issue in rbuilder. When the constraint spammer is stopped, the constraint-server logs show that rbuilder does not retrieve constraints for every block. As a result, constraints are only processed for some blocks instead of consistently for each one.
+
+```
+ERROR tokio-runtime-worker ThreadId(12) Failed to submit blocks with proofs: No signed constraints found for slot 43
+ERROR tokio-runtime-worker ThreadId(12) Failed to submit blocks with proofs: No signed constraints found for slot 46 
+ERROR tokio-runtime-worker ThreadId(12) Failed to submit blocks with proofs: No signed constraints found for slot 49
+```