Update README

README.md

 # Typon compiler
 
-This repository hosts the source code of the Typon compiler and standard library.
+Typon is a two-part project to bring practical GIL-free concurrency to Python:
+1. [`typon-concurrency`](https://lab.nexedi.com/typon/typon-concurrency), a C++ concurrency runtime
+2. typon-compiler (this repository), a compiler from Python syntax into C++
 
 ## Directory structure
 
-- `docs`: documentation
-- `include`: standard library and compiler primitives/intrisics
-- `runtime`: concurrency runtime (Git submodule)
-- `trans`: transpiler 
+### `docs`, documentation
+
+Currently using Sphinx.
+
+### `include`, standard library and compiler primitives/intrisics
+
+TODO.
+
+### `runtime`, concurrency runtime (Git submodule)
+
+See the [runtime repository](https://lab.nexedi.com/typon/typon-concurrency).
+
+### `trans`, transpiler 
+
+This repository, TODO.
 
 ## Development setup