Add a README.md to go with the test.

espresso-tests/README.md

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+# Espresso Migration
+
+This document contains details surrounding the test migrating an exsisting Arbitrum Orbit chain to use the nitro-espresso-integration, and be compatible with the Espresso network.
+
+## Running the test
+
+Run the test by navigating to nitro-testnode/espresso-tests and run ./migration-test.bash
+
+
+## Steps related to upgrade in production
+
+Many of the steps in the test are nearly identical to the steps needed to upgrade an orbit network to be compatible with the espresso network.
+
+Any commands in the migration-test.bash file that have comments above them prefixed with the string `** Essential migration step **` are core parts of the migration.
+
+E.g.
+```
+# ** Essential migration step ** Forge script to deploy new OSP entry. We do this to later point the rollups challenge manager to the espresso integrated OSP.
+forge script --chain $PARENT_CHAIN_CHAIN_ID contracts/parent-chain/contract-upgrades/DeployEspressoOsp.s.sol:DeployEspressoOsp --rpc-url $PARENT_CHAIN_RPC_URL --broadcast -vvvv
+```
+
+ Other steps, such as noting contract addresses, are technically part of these essential core steps. However, these steps are not marked with " ** Essential migration step ** ". In a real migration, these steps will likely not occur in a single bash script, or necessarily have the same process.
+
+These steps can be done manually while preparing the `** Essential migration step **` steps in whichever manner makes sense to the operators of the network doing their migration. Therefore they are marked with `* Essential migration sub step * `, and specific context is given as to how these steps may be different for operators.
+
+## Non upgrade related steps
+
+Steps that are not directly related to a real world example of this upgrade will be unmarked. That is comments about these steps will contain neither `** Essential migration step **` or `* Essential migration sub step *`