Correct formatting of chapter 21 readme.

Author: Stratus3D

chapter_21/README.md

@@ -1,9 +1,9 @@
-#Exercises for Chapter 21
+# Exercises for Chapter 21
 
-##1. Add an error to dict.erl. Compile the module.
+## 1. Add an error to dict.erl. Compile the module.
 I have altered `dict.erl` so a certain line in it will cause it to crash. `dict.erl` is stored in the `exercise_1/` directory.
 
-##2. Write a simple test module that calls dict in various ways to uncover the error.
+## 2. Write a simple test module that calls dict in various ways to uncover the error.
 Test module is in `exercise_2/`. In this directory, run:
 
     erlc exercise_1/dict.erl exercise_2/dict_test.erl
@@ -14,7 +14,7 @@ And then in the Erlang console run the tests:
     dict_test:test().
 
 
-##3. Use the code coverage tool to see how many lines in the dict module are being executed by the test module.
+## 3. Use the code coverage tool to see how many lines in the dict module are being executed by the test module.
 The code coverage script is stored in the `exercise_3` directory. To run the code coverage analysis compile the code and start an erl console:
 
     erlc exercise_1/dict.erl exercise_2/dict_test.erl exercise_3/dict_test_coverage.erl
@@ -24,7 +24,7 @@ And then in the Erlang console run the command to generate the code coverage res
 
     dict_test_coverage:coverage().
 
-##4. Use the dbg module to find the error in the dict module
+## 4. Use the dbg module to find the error in the dict module
 The dbg script is stored in the `exercise_4` directory. To run the dbg tracing on the dict module compile the code and start an erl console:
 
     erlc exercise_1/dict.erl exercise_2/dict_test.erl exercise_3/dict_test_coverage.erl