Update README.md

peripherals/tx_wrapper/README.md

@@ -1,5 +1,11 @@
 # evm_poc_tx_wrapper
 
+## Prerequisite
+You need to have a miner account (for example: a123) with enough CPU & NET resource. Then open the evm account balance
+```
+./cleos push action eosio.evm open '{"owner":"a123"}' -p a123
+```
+
 ## Build
 ```
 yarn
@@ -15,9 +21,16 @@ EOS_RPC="http://127.0.0.1:8888|http://192.168.1.1:8888"
 EOS_KEY="5KQwrPbwdL6PhXujxW37FSSQZ1JiwsST4cqQzDeyXtP79zkvFD3"
 HOST="0.0.0.0"
 PORT="18888"
-EOS_EVM_ACCOUNT="evmevmevmevm"
+
+# the evm contract account, eosio.evm for testnet & mainnet.
+EOS_EVM_ACCOUNT="eosio.evm"
+
+# the miner account
 EOS_SENDER="a123"
+
+# the miner's permission to use 
 EOS_PERMISSION="active"
+
 EXPIRE_SEC=60
 ```