Enhance README with more details on key files

Expanded details about main.py and srcastro.

Author: jacklowrie

README.md

@@ -7,7 +7,8 @@ This Demos how to set up a python coding challenge that runs locally in the brow
 
 ## Key files
 
-- `srcastro`: contains web-related assets.
-- `srcpy`: contains source python programs that run via pyscript
-  - `main.py`: dispatches new worker threads to evaluate challenge code (any time the "run tests" button is clicked)
+- `srcpy/`: contains source python programs that run via pyscript
+  - `main.py`: dispatches new worker threads to evaluate challenge code (any time the "run tests" button is clicked). Also, registers event hook for that button, and displays results of the run from the worker thread on the page.
   - `worker.py`: Worker thread program. Evaluates the submitted code for rules, then runs the implementation against test cases.
+- `srcastro/`: contains web-related assets (content, html, etc).
+