Add power operator in introduction

introduction/introduction/introduction.tex

@@ -409,6 +409,14 @@ IPython 6.1.0 -- An enhanced Interactive Python. Type '?' for help.
   \begin{pythonout}
 42
   \end{pythonout}
+  \\
+
+  \begin{pythonin}{python}
+2 ** 3
+  \end{pythonin}
+  \begin{pythonout}
+8
+  \end{pythonout}
  \end{ipython}
 \end{pframe}