Merge: Automatic publication to prov store and update of README files

Following #86 (and discussions at #84), for each example document (in `examples/spm` and `examples/fsl`) only the `provn` serialisation is stored in the `nidm` repository. A `README` is provided for each `provn` file providing a link to a [public document in the Prov Store](https://provenance.ecs.soton.ac.uk/store/public/), where alternative serialisations (ttl, json, svg) can be found.

This pull request provides a script to be called after each change in the data model to automatically:
1. upload the modified documents to the Prov Store and 
2. update the REAMEs accordingly.


perhaps pick these up from environment variables or a file.