Fix bulk document importer GET requests

From https://doc.nuxeo.com/nxdoc/nuxeo-bulk-document-importer/

The Quick Start doesn't make much sense for users.

GET http://NUXEO_SERVER/nuxeo/site/fileImporter/run?targetPath=/default-domain/workspaces/some-workspace&inputPath=/path/to/import&batchSize=10&interactive=false&nbThreads

For it to truly be a Quick Start:

• all the REST calls should be in the form of curl requests
• the &nbThreads should either be removed or given a value
• user should only have to copy/paste and replace the server and paths to proceed

See https://github.com/nuxeo/nuxeo-platform-importer/tree/master/nuxeo-importer-stream#two-steps-import-generate-and-import-documents-with-blob