Add description to topics in README.

Author: drvinceknight

README.md

@@ -6,6 +6,8 @@
 Topics covered:
 
 1. [Basic Python](./nbs/00 - Studying Mathematics with Python.ipynb)
-2. [Using Sympy](./nbs/01 - Symbolic mathematics with Sympy.ipynb)
-3. [Using Numpy](./nbs/02 - Linear algebra with Numpy.ipynb)
-4. [Using Pandas](./nbs/03 - Data analysis with Pandas.ipynb)
+2. [Using Sympy](./nbs/01 - Symbolic mathematics with Sympy.ipynb) for symbolic
+   mathematics.
+3. [Using Numpy](./nbs/02 - Linear algebra with Numpy.ipynb) for linear algebra.
+4. [Using Pandas](./nbs/03 - Data analysis with Pandas.ipynb) for basic handling
+   of data.