docs: make documentation on how to use the API. "First steps with Argus"

[katsel]

Put together a very basic tutorial of things to do after having set up Argus!

Intended for onboarding new developers, showcasing some basic features and principles, and give users and devs practical examples of how to get things done.

Could include:

• creating fake incidents
• getting/using auth tokens
• changing passwords and user data
• POSTing and GETting data from/to the API
• small hints like: make JSON output readable with jq

If it is going to be me doing this, this will be console-based and with cURL. Open to suggestions.

[katsel]

An "how to use the API" tutorial will be needed now that drf-spectacular is implemented. It should mention where to find the auto-generated spectacular-api-docs in the API. We may need to discuss

• if it is possible,
• if we want to,
• and how to

include the auto-generated API-docs on readthedocs too.