Add more info and example config to README

[will-moore]

See https://trello.com/c/2bBx96kX/23-mapr-installation

Make the install docs more user-friendly with some background info and example how to set-up Map Annotations to work with a given config.

Staged at https://github.com/will-moore/omero-mapr/tree/README_more_info

TODO: I'll also look at using mapr to search for client-created Map Annotations as suggested elsewhere...

[will-moore]

After following workflow in README for image in Project/Dataset, I see

[joshmoore]

The travis failure is due to a change in upstream pytest versions which I've fixed elsewhere.

[will-moore]

NB: I noticed that this user might benefit from using mapr. https://www.openmicroscopy.org/community/viewtopic.php?f=4&t=8446&p=19039 Can post a suggestion to look once this PR is merged.

[will-moore]

More screenshots to add for usage of "client" map annotations:

[jburel]

@will-moore

31 has been merged

7816340 is already in #31

[joshmoore]

Green! :tada: