Add chapters to readme

Author: Rion5

readme.md

@@ -3,10 +3,21 @@
 1. **Python Data Science Toolbox**
    * Part I
    * [Part II](https://github.com/Rion5/Python_Data_Science/tree/master/Python_Data_Science_Toolbox/Python_Data_Science_Toolbox_pt2)
+     * Iterators
+     * List Comprehensions and Generators
 2. **Importing Data in Python**
    * [Part I](https://github.com/Rion5/Python_Data_Science/tree/master/Importing_Data/Importing_Data_in_Python_pt1)
+     * Importing Flat Files
+     * Importing Other File Types
+     * Working With Relational Databases
    * [Part II](https://github.com/Rion5/Python_Data_Science/tree/master/Importing_Data/Importing_Data_in_Python_pt2)
+     * Importing Data from the Internet
+     * Importing Data from APIs and JSON
 3. **[Cleaning Data in Python](https://github.com/Rion5/Python_Data_Science/tree/master/Cleaning_Data_in_Python)**
+    * Exploring Data
+    * Tidying Data for Analysis
+    * Combining Data for Analysis
+    * Cleaning Data for Analysis
 4. **pandas DataFrame**
    * [pandas Foundations](https://github.com/Rion5/Python_Data_Science/tree/master/pandas/pandas_Foundations)
      * Common Commands