Update README

README.md

@@ -25,6 +25,22 @@ the software to try it out. You can also run Synit inside a virtual machine.
 See the [installation instructions](https://synit.org/book/install.html) for a list of supported
 devices.
 
-# Documentation
+## Documentation
 
 See [the Synit Manual](https://synit.org/book/).
+
+## Repository contents
+
+ - [`synit-pid1/`](synit-pid1/) is a small, simple Rust program implementing a minimal PID1 for
+   the Synit system.
+
+ - [`protocols/schemas/`](protocols/schemas/) contains schema definitions for the protocols
+   used among the components of the system.
+
+ - [`packaging/`](packaging/) contains Alpine (PostmarketOS) packaging scripts and supporting
+   files for Synit components. The packages themselves live in
+   [`packaging/packages/`](packaging/packages/). A particularly interesting package is
+   [`synit-config`](packaging/packages/synit-config/).
+
+ - [`scripts/`](scripts/) contains support scripts for uploading and installing Synit packages
+   on a target device.