Update README.md

Author: evanp

README.md

@@ -83,6 +83,8 @@ Extensions are documented on the [Extensions registry](https://www.w3.org/wiki/A
 
 The [Fediverse Enhancement Proposals](https://codeberg.org/fediverse/fep) process is a lightweight collaboration process for creating and documenting Activity Streams 2.0 extensions (and other changes to the Fediverse). It's a good place to start if you're considering a backwards-compatible change.
 
+There are many ideas for backwards-compatible changes to ActivityPub that have not yet been written up as a FEP or other document. These are marked [Needs FEP](https://github.com/w3c/activitystreams/issues?q=is%3Aopen+is%3Aissue+label%3A%22needs-fep%22) in the ActivityPub GitHub issue repository, and contributors are welcome to [submit a FEP](https://codeberg.org/fediverse/fep/src/branch/main#submitting-a-fep) on the topic. Note that issues may be closed without the FEP being created; that does not mean that the FEP is no longer needed.
+
 Extensions that become popular can be integrated into the AS2 vocabulary document, making them practically part of the spec. The [Extensions Policy](https://swicg.github.io/extensions-policy/) describes how to propose extensions for inclusion in AS2.
 
 Future versions of the AS2 specification(s) may include popular extensions as part of the core specs; see below.