docs: update the top-level README.md to say a bit more. (#4)

README.md

@@ -2,4 +2,27 @@
 
 Home of the Shorebird Tools 🐦
 
-🚧 Under construction... 🚧
+## Status
+
+We're in the process of converting the quick demos written by one person, into a
+multi-contributor project usable by others. Previous demo code can be found at:
+https://github.com/shorebirdtech/old_repo
+
+## Usage
+
+Instructions coming soon.
+
+## Contributing
+
+If you're interested in contributing, please join us on
+[Discord](https://discord.gg/9hKJcWGcaB).
+
+## License
+
+Shorebird projects are licensed for use under either Apache License, Version 2.0
+(LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0) MIT license
+(LICENSE-MIT or http://opensource.org/licenses/MIT) at your option.
+
+See our license philosophy for more information on why we license files this
+way:
+https://github.com/shorebirdtech/handbook/blob/main/engineering.md#licensing-philosophy