docs(contracts): state the ABI-only source-of-truth and regeneration story

Make the package answer the reviewer's question where a maintainer will
actually look: the artifacts are ABI-only with no in-tree Solidity source
(and never had one — the removed compile targets only ever built the deleted
erc20 .sols), the embedded JSON is the source of truth, and changes go
through editing the JSON plus the guard test that pins signatures, addresses,
and the bytecode-less nature.

Signed-off-by: puneetmahajan <59960662+puneet2019@users.noreply.github.com>

Author: puneet2019

contracts/erc721NonTransferable.go

@@ -1,3 +1,12 @@
+// Package contracts holds the compiled-contract artifacts moca keepers encode
+// EVM calls against (mirroring cosmos/evm's top-level contracts/ package).
+//
+// The artifacts here are ABI-only and have no in-tree Solidity source: the
+// embedded JSON is the source of truth (greenfield heritage; it carries no
+// bytecode and nothing ever deploys it — keepers only encode calldata toward
+// fixed addresses). There is deliberately no compile/regenerate target; to
+// change an artifact, edit the JSON and update the guard test that pins its
+// call signatures, addresses, and bytecode-less nature.
 package contracts
 
 import (