Update readme.

README.md

@@ -2,14 +2,26 @@
 
 [![Build Status](https://github.com/dmackdev/pubsubman/workflows/CI/badge.svg)](https://github.com/dmackdev/pubsubman/actions?workflow=CI)
 
-A GUI client for GCP Pub/Sub, built in Rust with `egui`.
+A GUI client for GCP Pub/Sub, built in Rust with [egui](https://github.com/emilk/egui).
 
 <p align="center">
   <img src="./media/messages_view.png" alt="Messages View Screenshot"/>
 </p>
 
+## Features
+
+- [x] Pull or stream messages from topics on automatically created, dedicated subscriptions.
+- [x] Interactive JSON visualisation for message data.
+- [x] Copy message data JSON structures to the clipboard.
+- [x] Filter received messages by ID or JSON contents.
+- [x] Publish new messages, and republish previously received messages.
+- [x] Persistence of received messages.
+- [x] Option to delete created subscriptions when quitting the app.
+
 ## Usage
 
+`pubsubman` internally uses the [google-cloud-pubsub](https://crates.io/crates/google-cloud-pubsub) crate. As such, the `GOOGLE_APPLICATION_CREDENTIALS` and `GOOGLE_APPLICATION_CREDENTIALS_JSON` environment variables are respected for authenticating against a GCP Project.
+
 If wishing to use a locally running GCP Pub/Sub emulator, ensure your `PUBSUB_EMULATOR_HOST` environment variable is set, e.g:
 
 ```