Example on how one would use a Reader class

[ssomnath]

This example should show how a user would go about using a Reader class:

1. First pick the appropriate Reader class. We can replace this manual step with a read() function which would automatically find which Reader to use
2. Then, pass the file to instantiate the Reader object
3. Call the my_reader.read() function to get back one or more sidpy.Dataset objects
4. Show the user that this sidpy.Dataset object has the following:
   1. Raw data - by visualizing the data
   2. Metadata
5. How how the user could optionally use pyNSID or pyUSID to write the sidpy.Dataset object(s) to HDF5 if the user wanted to exchange information with other researchers.
   1. Show the tree structure within the HDF5 file showing where the data has been written to. No need to visualize again.
   2. Show that the metadata too has been safely captured
   3. Show that any ancillary dataset(s) have also been written to HDF5

[ssomnath]

@gduscher - You have largely addressed this issue with your last pull request #2. Awesome job! I think that only a handful of things are necessary to complete this example. We want this example to be fully self contained. Provide a small dm3 file in a data folder of this repository for demonstration, instead of expecting the user to provide a file. You can certainly make a note that the users should replace the file path or use the pyQt5 file opener (present in sidpy) to open their own dm3 files. Also in general, avoid file interface functions in these examples, since these are not interactive.

Do let me know if you have any questions