Adding matlab file to manifest and updating import statement

MANIFEST.in

@@ -1,4 +1,5 @@
 include README.md
 include requirements.txt
 include plotting.txt
-include logo_hi.png
+include logo_hi.png
+include docs/source/nb_examples/SonarAlt.mat

gps_helper/simulator.py

@@ -1,6 +1,10 @@
 import numpy as np
-from scipy.io import loadmat
 import os
+import warnings
+try:
+    from scipy.io import loadmat
+except ImportError:
+    warnings.warn("scipy was not found; used for GetSonar")
 
 
 class GetVoltage(object):
@@ -140,6 +144,8 @@ class GetSonar(object):
     A class for playing back sonar altitude measurements as found in Kim 2.4
     and later used in Kim 11.5
 
+    This example requires the scipy package to load a .mat file.
+
     Mark Wickert December 2017
     """