contracts-bedrock: update readme (#10636)

The Custom Gas Token feature is a Beta feature of the MIT licensed OP Stack.
While it has received initial review from core contributors, it is still undergoing testing, and may have bugs or other issues.

Also cleanup some old information

packages/contracts-bedrock/README.md

@@ -23,6 +23,7 @@ High-level information about these contracts can be found within this README and
   - [Style Guide](#style-guide)
 - [Deployment](#deployment)
   - [Configuration](#configuration)
+    - [Custom Gas Token](#custom-gas-token)
   - [Execution](#execution)
   - [Deploying a single contract](#deploying-a-single-contract)
 - [Testing](#testing)
@@ -277,18 +278,22 @@ values are addresses. This works well with the JSON files in `superchain-ops`.
 ### Configuration
 
 Create or modify a file `<network-name>.json` inside of the [`deploy-config`](./deploy-config/) folder.
-By default, the network name will be selected automatically based on the chainid. Alternatively, the `DEPLOYMENT_CONTEXT` env var can be used to override the network name.
-The spec for the deploy config is defined by the `deployConfigSpec` located inside of the [`hardhat.config.ts`](./hardhat.config.ts).
+Use the env var `DEPLOY_CONFIG_PATH` to use a particular deploy config file at runtime.
+
+#### Custom Gas Token
+
+The Custom Gas Token feature is a Beta feature of the MIT licensed OP Stack.
+While it has received initial review from core contributors, it is still undergoing testing, and may have bugs or other issues.
 
 ### Execution
 
 Before deploying the contracts, you can verify the state diff produced by the deploy script using the `runWithStateDiff()` function signature which produces the outputs inside [`snapshots/state-diff/`](./snapshots/state-diff).
 Run the deployment with state diffs by executing: `forge script -vvv scripts/Deploy.s.sol:Deploy --sig 'runWithStateDiff()' --rpc-url $ETH_RPC_URL --broadcast --private-key $PRIVATE_KEY`.
 
-1. Set the env vars `ETH_RPC_URL`, `PRIVATE_KEY` and `ETHERSCAN_API_KEY` if contract verification is desired
+1. Set the env vars `ETH_RPC_URL`, `PRIVATE_KEY` and `ETHERSCAN_API_KEY` if contract verification is desired.
+1. Set the `DEPLOY_CONFIG_PATH` env var to a path on the filesystem that points to a deploy config.
 1. Deploy the contracts with `forge script -vvv scripts/Deploy.s.sol:Deploy --rpc-url $ETH_RPC_URL --broadcast --private-key $PRIVATE_KEY`
    Pass the `--verify` flag to verify the deployments automatically with Etherscan.
-1. Generate the hardhat deploy artifacts with `forge script -vvv scripts/Deploy.s.sol:Deploy --sig 'sync()' --rpc-url $ETH_RPC_URL --broadcast --private-key $PRIVATE_KEY`
 
 ### Deploying a single contract