Create section with API usage examples

[giohappy]

This guide should describe:

• Authentication
  • Basic Auth
  • Bearer token / apikey parameter (explaining how to obtain the token from Django admin or /api/o/v4/userinfo)
• Resource listing and filtering
• Update a resource
• Upload a dataset (ask @mattiagiupponi to give a help on this)
• Upload a document
• Download a resource (navigating the download links inside the resource response body)
• Delete a resource
• Get the list of users and groups
• Manage permissions

Bonus: create a PostMan collection with examples for master demo (with a demo user)

[gannebamm]

The auth section lacks how to optain the bearer token

Bearer token / apikey parameter (explaining how to obtain the token from Django admin or /api/o/v4/userinfo)

Not sure if it missing in the docs or missing as functionality in the api

Upload a document

Is not part of the PR

[gannebamm]

Found the doc upload section:

At the moment documents can’t be uploaded through the API. This will probably change in the future.

OK, that's a pity. It is the api than

[giohappy]

@gannebamm FYI a simple implementation of document upload via API is now available. Example in the doc is still missing though #266