Add note about file structure

README.md

@@ -1,2 +1,8 @@
 # polyproto
 Specification documents and API documentation for the polyproto federated messaging protocol
+
+## File structure
+
+The `/docs` folder contains the specification documents for the polyproto protocol. The `docs/APIs` folder contains the API documentation for the polyproto-core and polyphony-chat reference implementation.
+
+The `/snippets` folder contains snippets of text that are used in multiple places in the documentation. This is to ensure consistency across the documentation. Any error messages that are used in multiple places are also stored here, in the `/snippets/errors` folder.