OEV gateway migration guide entry (#1223)

docs/airnode/v0.11/reference/migration.md

@@ -29,6 +29,10 @@ such as airnode-deployer, airnode-admin, etc., and new features.
 
 2. `nodeSettings.nodeVersion` updated to "0.11.0".
 
+3. Pre/post-processing is dropping version of the processing environment.
+
+4. Section `nodeSettings.oevGateway` was added.
+
 ## Details
 
 1. `ois[n].oisFormat`
@@ -87,9 +91,33 @@ from 14 to 18.
 }
 ```
 
+4. With the new OEV gateway feature there's a new section in the configuration
+   file for it. The new section `nodeSettings.oevGateway` needs to be added in
+   order for the configuration file to be valid.
+
+```diff
+{
+  "httpSignedDataGateway": {
+    "enabled": false
+  },
++ "oevGateway": {
++   "enabled": false
++ },
+  "logFormat": "plain",
+  "logLevel": "INFO",
+}
+```
+
+Read the
+[OEV gateway documentation](../grp-providers/guides/build-an-airnode/oev-gateway.md)
+to learn more about this feature.
+
 ## New features
 
 - The Node.js version of Airnode was upgraded from 14 to 18.
 - The `coingecko-signed-data` and `coingecko-testable` HTTP gateway
   `airnode-examples` integrations have been combined into a single
   `coingecko-http-gateways` integration.
+- There's a new gateway available called the OEV gateway. You can read more
+  about this feature in its
+  [documentation](../grp-providers/guides/build-an-airnode/oev-gateway.md).