Fix README table

Author: William Lubanovic

README.md

@@ -5,23 +5,23 @@ introducingpython
 This repository contaisn the programs featured in
 "An introduction to Python".
 
-dir     chapter
----     -------
-intro   1. A taste of Py
-        2. Py ingredients: numbers, strings, and variables
-        3. Py filling: lists, tuples, dictionaries, and sets
-        4. Py crust: code structures
-boxes   5. Py boxes: modules, packages, and programs
-        6. Oh oh: objects and classes
-        7. Mangle data like a pro
-storage 8. Data has to go somewhere
-web     9. The web, untangled
-sys    10. Systems
-net    11. Concurrency and networks
-dev    12. Be a pythonista
-art     A. Py art
-bus     B. Py at work
-        C. Py sci
-        D. Install Python 3
-        E. Answers to exercises
-        F. Cheatsheets
+|directory|chapter|
+|---|---|
+|intro|  1. A taste of Py
+|     |  2. Py ingredients: numbers, strings, and variables
+|     |  3. Py filling: lists, tuples, dictionaries, and sets
+|     |  4. Py crust: code structures
+|boxes|  5. Py boxes: modules, packages, and programs
+|     |  6. Oh oh: objects and classes
+|     |  7. Mangle data like a pro
+|storage|8. Data has to go somewhere
+|web  |  9. The web, untangled
+|sys  | 10. Systems
+|net  | 11. Concurrency and networks
+|dev  | 12. Be a pythonista
+|art  |  A. Py art
+|bus  |  B. Py at work
+|     |  C. Py sci
+|     |  D. Install Python 3
+|     |  E. Answers to exercises
+|     |  F. Cheatsheets