Fix warning on external links due to lowercase extension

docs/source/file_read/matnwb/nwbfile.rst

@@ -5,7 +5,7 @@ Using the NwbFile Class
 
 The NwbFile class represents the root object for the NWB file and consists of properties and values which map indirectly to the internal HDF5 dataset.
 
-.. image:: /img/NwbFile.png
+.. image:: /img/matnwb_NwbFile.png
 
 In most cases, the types contained in these files were generated by the embedded NWB schema in the file (or separately if you opted to generate them separately). These types can be traversed using regular MATLAB syntax for accessing properties and their values.
 
@@ -20,11 +20,11 @@ The NwbFile also allows for searching the entire NWB file by type using its ``se
 
 You can search for only the class name:
 
-.. image:: /img/searchForExample.png
+.. image:: /img/matnwb_searchForExample.png
 
 Or use the ``'includeSubClasses'`` optional argument to search all subclasses:
 
-.. image:: /img/searchForExample-withSubclassing.png
+.. image:: /img/matnwb_searchForExample-withSubclassing.png
 
 .. note::