Update README.md

Author: André Gaul

README.md

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 # PseudoPy
 
 PseudoPy computes and visualizes the pseudospectrum of a matrix. It is a Python version of the original [eigtool](http://www.cs.ox.ac.uk/pseudospectra/eigtool/) by Thomas G. Wright. The algorithms used in this package can be found in the book [Spectra and pseudospectra](http://press.princeton.edu/titles/8113.html) by [Nick Trefethen](http://www.maths.ox.ac.uk/people/profiles/nick.trefethen) and [Mark Embree](http://www.caam.rice.edu/~embree/).
+
+## Example
+The pseudospectrum of the Grcar matrix looks like this:
+
+![Pseudospectrum of Grcar matrix](grcar.png)
+
+The above figure can be created by running
+```python
+from pseudopy import demo
+demo.grcar_demo()
+```
+and the corresponding code of `grcar_demo` can be found in [pseudopy/demo.py](pseudopy/demo.py).