Add matplotlib to readme. (drvinceknight#16)

Author: drvinceknight

README.md

@@ -7,12 +7,14 @@
 
 ## Topics covered:
 
-1. [Basic Python](./nbs/00-Studying-Mathematics-with-Python.ipynb)
-2. [Using Sympy](./nbs/01-Symbolic-mathematics-with-Sympy.ipynb) for symbolic
+1. [Basic Python](00-Studying-Mathematics-with-Python.ipynb)
+2. [Using Sympy](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.
+3. [Using Numpy](02-Linear-algebra-with-Numpy.ipynb) for linear algebra.
+4. [Using Pandas](03-Data-analysis-with-Pandas.ipynb) for basic handling of
+   data.
+5. [Using matplotlib for visualisation](04-Visualisation-with-matplotlib.ipynb)
+   for visualisation.
 
 ## Creating the pdfs and tex files: