Document how to disable challenges

[commjoen]

We need to add a section in the readme that explains how you can disable/remove a challenge:

In short: you have to remove the challenge from https://github.com/OWASP/wrongsecrets/blob/c981b2e0557301ab30a4b1a294de7080ec54ac49/src/main/resources/wrong-secrets-configuration.yaml and then you can rebuild with ./mvnw clean install and then build your own container from it to distribute somewhere and that is how you can host the challenge. For the building of the container, we need to describe how you can build that container to push it to a repo you control.

[djvinnie]

Please assign this issue to me.

[commjoen]

The challenge is yours sir! Welcome!