add example to documentation

README.md

@@ -30,6 +30,20 @@ What this program can do is produce these two automata, not only for the equilat
 
 See `example.py`. The function `generate_automaton_coxeter_matrix` takes as argument the [Coxeter matrix] of the desired group and a boolean determining which of the two automata is generated. It returns the automaton as an adjacency list. In addition, the function `enumerate_group` can compute all group elements up to a given word length, including the edges of the Cayley graph. To do this, it uses both automata.
 
+For example, the following code would give us the first of the two automata above:
+
+    #!/usr/bin/python
+
+    import coxeter_automaton
+
+    coxeter_matrix = [[1, 3, 3],
+                      [3, 1, 3],
+                      [3, 3, 1]]
+
+    graph = coxeter_automaton.generate_automaton_coxeter_matrix(coxeter_matrix, lex_reduced = False)
+
+    print(graph)
+
 For a more human-readable output, `dot_graph.py` generates dot files, which can be used as input to [Graphviz] to render the graph as a PDF file. The resulting images are not quite as nice as the manually drawn ones above, but usually good enough to be useful.
 
 [Brink-Howlett]: https://link.springer.com/article/10.1007/BF01445101