Invalid example URL for loading projects from DB in README

[hustodemon]

Hello everyone,

when testing loading projects from the DB, I got a 404 from the qwc-qgis-server when using the suggested URL (http://localhost:8001/qgis/pg/public/myproject). Changing to http://localhost:8001/ows/pg/public/myproject worked.

It seems the URL_PREFIX had changed in the past, but the README was not updated.

Suggested fix: #9

[tpo]

I'm closing this ticket, since #9 was merged, I hope that's fine, otherwise please reopen with justification