Add docs for DataCollection.plot_missing_data

Author: JamesWrigley

docs/_static/plot_missing_data.png

@@ -365,6 +365,14 @@ Missing data does not necessarily mean that something has gone wrong:
 some devices send data at less than 10 Hz (the train rate), so they always
 have gaps between updates.
 
+You can use :meth:`DataCollection.plot_missing_data` to quickly visualize
+sources that have missing data:
+
+.. class:: DataCollection
+   :noindex:
+
+   .. automethod:: plot_missing_data
+
 Data problems
 -------------
 

docs/reading_files.rst

@@ -1321,6 +1321,10 @@ def keys_detail(s, keys, prefix=''):
     def plot_missing_data(self, min_saved_pct=95, expand_instrument=False):
         """Plot sources that have missing data for some trains.
 
+        Example output:
+
+        .. image:: _static/plot_missing_data.png
+
         Parameters
         ----------