docs: admin JWT creation

[ho-229]

The README currently states that the admin JWT is set via an environment variable. However, in practice, the admin JWT is generated by a hidden API endpoint at /jwt/create. This discrepancy can cause confusion for users and developers trying to configure or use the system.

[LemonHX]

this is an internal API which could be changed in close future

[ho-229]

but JWT_TOKEN environment variable was not work like README noted