Update README.md (#460)

README.md

@@ -6,6 +6,21 @@
 
 **WARNING: All interfaces are subject to change.**
 
+## Can I use this?
+
+In order to generate a usable smithy client you must provide a [protocol definition](https://github.com/aws/smithy-go/blob/main/codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/integration/ProtocolGenerator.java),
+such as [AWS restJson1](https://smithy.io/2.0/aws/protocols/aws-restjson1-protocol.html),
+in order to generate transport mechanisms and serialization/deserialization
+code ("serde") accordingly.
+
+The code generator does not currently support any protocols out of the box,
+therefore the useability of this project on its own is currently limited.
+Support for all [AWS protocols](https://smithy.io/2.0/aws/protocols/index.html)
+exists in [aws-sdk-go-v2](https://github.com/aws/aws-sdk-go-v2). We are
+tracking the movement of those out of the SDK into smithy-go in
+[#458](https://github.com/aws/smithy-go/issues/458), but there's currently no
+timeline for doing so.
+
 ## License
 
 This project is licensed under the Apache-2.0 License.