docs: Update migration notes. (#149)

README.md

@@ -112,8 +112,8 @@ Contributions are welcome! Please refer to our [CONTRIBUTING](https://github.com
 
 # Migrating from Indexer 2.x
 
-Conduit can be used to populate data from an existing [Indexer 2.x](https://github.com/algorand/indexer/) deployment as part of upgrading to Indexer 3.x.
+Conduit can be used to populate data from an existing [Indexer 2.x](https://github.com/algorand/indexer/) deployment as part of upgrading to Indexer 3.x. The v3 API is 100% backwards compatible with the v2 API.
 
-We will continue to maintain Indexer 2.x for the time being, but encourage users to move to Conduit. It provides cost benefits for most deployments in addition to greater flexibility.
+We will continue to maintain Indexer 2.x up through November 1. From that point onward, subsequent consensus upgrades will only be compatible with Indexer 3.x when paired with Conduit.
 
 To migrate, follow the [Using Conduit to Populate an Indexer Database](./docs/tutorials/IndexerWriter.md) tutorial. When you get to the step about setting up postgres, substitute your existing database connection string. Conduit will read the database to initialize the next round.