Readme mentions non existing endpoints

[g-fabiani4-unipi]

The readme mentions some non existing endpoints:

• health (fixed in Fix health endpoint #1)
• load_graph: as a result the whole file-based workflow description is non-sensical

I can remove the mentions of load_graph from the readme and rewrite the file-based workflow in a manner that makes sense. If I understand correctly the idea is to:

1. Copy the json file in graph_storage
2. set the graph as default
3. success!