README: Add usage section

README.md

@@ -6,3 +6,30 @@ Our [next steps](https://www.cython.plus/P-CYP-Roadmap) include with writing a m
 
 To drive this effort I'm writing a very basic HTTP server in Cython+, building everything I will need along the way.
 
+
+## Usage
+
+The repository looks like this:
+
+```
+- README.md
+- src/
+    - Makefile
+    - setup.py
+    - stdlib/
+        - *.pxd
+        - ...
+    - *.pyx
+    - ...
+- ...
+```
+
+Each `.pyx` file in `src` is a standalone demo.
+
+To run the demos (e.g. `helloworld.pyx`):
+
+```
+cd src
+make helloworld
+```
+