Add a README

* Use an environment variable to set EXECUTION_MANAGER_ADDRESS

OPTIMISM_README.md

@@ -0,0 +1,21 @@
+Running the Optimism Execution Manager Node:
+
+1. Build geth
+
+       $ go build
+
+2. Initialize the node
+
+       $ ./build/bin/geth init etc/optimism.json
+
+3. Import the signers private key (ask in Slack for the private key file):
+
+        $ ./build/bin/geth account import private_key.hex
+
+4. Deploy the Execution Manager (in [packages/ovm](https://github.com/op-optimism/optimistic-rollup/tree/master/packages/ovm))
+
+        $ yarn run deploy:execution-manager local
+
+5. Run geth
+
+        $ EXECUTION_MANAGER_ADDRESS=0xEB1Be3E5Ff32bd47D9589f3f1E73B1788F36639c ./build/bin/geth --datadir data  --syncmode 'full' --rpc --rpcaddr 'localhost'  --rpcapi 'eth,net' --networkid 12 --allow-insecure-unlock --gasprice '1' -unlock '0xAb521188aA30ccc4a88Ec9ea6BC55541b72eD1d3' --mine

core/vm/instructions.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"errors"
 	"math/big"
+	"os"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/math"
@@ -33,7 +34,7 @@ var (
 	tt255                    = math.BigPow(2, 255)
 	OvmSLOADMethodId         = hashSha3([]byte("ovmSLOAD()"))[0:4]
 	OvmSSTOREMethodId        = hashSha3([]byte("ovmSSTORE()"))[0:4]
-	OvmContractAddress       = common.FromHex("EB1Be3E5Ff32bd47D9589f3f1E73B1788F36639c")
+	OvmContractAddress       = common.FromHex(os.Getenv("EXECUTION_MANAGER_ADDRESS"))
 	errWriteProtection       = errors.New("evm: write protection")
 	errReturnDataOutOfBounds = errors.New("evm: return data out of bounds")
 	errExecutionReverted     = errors.New("evm: execution reverted")