note deploy gen-tx need rpc Indexer in docs

[rink1969]

I met a error when deploy script with ckb-cli follow docs
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$ ./ckb-cli deploy gen-txs --deployment-config ./deployment.toml --migration-dir ./ --from-address ckt1qzda0cr08m85hc8jlnfp3zer7xulejywt49kt2rr0vthywaa50xwsq2prryvze6fhufxkgjx35psh7w70k3hz7c3mtl4d --info-file deploy-tx.json
jsonrpc error: Method not found: Method not found
···

then I found to fix it need add Indexer in rpc modules at file ckb.toml, but it haven't mentioned in any docs.