docs: explain how to find SOAR_URL

[P-r-e-m-i-u-m]

This adds a small troubleshooting note for the SecOps SOAR SOAR_URL setup path.

What changed:

• documents the Failed to fetch valid scopes from SOAR startup error
• clarifies that SOAR_URL should be the SOAR base URL, not the Backstory URL
• adds two practical ways to find the correct base URL from the SOAR UI
• links the SecOps SOAR server page back to the usage guide

Closes #96

Validation:

• Ran python -m sphinx -b html docs docs\_build\html successfully.
• The build still reports existing documentation warnings unrelated to this change, mostly missing toctree entries and pre-existing cross-reference warnings.