[Minor] GUI for matplotlib to run examples (#323)

* Proposal to add pyqt5 as GUI to run examples correctly

* Add note about matplotlib gui backend instead

Author: mvargas33

examples/plot_metric_learning_examples.py

@@ -15,7 +15,11 @@
 ######################################################################
 # Imports
 # ^^^^^^^
+# .. note::
 #
+#     In order to show the charts of the examples you need a graphical
+#     ``matplotlib`` backend installed. For intance, use ``pip install pyqt5``
+#     to get Qt graphical interface or use your favorite one.
 
 from sklearn.manifold import TSNE
 

examples/plot_sandwich.py

@@ -6,6 +6,13 @@
 Sandwich demo based on code from http://nbviewer.ipython.org/6576096
 """
 
+######################################################################
+# .. note::
+#
+#     In order to show the charts of the examples you need a graphical
+#     ``matplotlib`` backend installed. For intance, use ``pip install pyqt5``
+#     to get Qt graphical interface or use your favorite one.
+
 import numpy as np
 from matplotlib import pyplot as plt
 from sklearn.metrics import pairwise_distances