Update documentation about imc-config secrets namespace

[benedikt-bartscher]

the readme should mention that the imc-config secret is only read from the namespace where ingressmonitorcontroller is deployed (by default stakater-ingress-monitor-controller).

[github-actions]

This issue is stale because it has been open for 60 days with no activity.

[github-actions]

This issue was closed because it has been inactive for 30 days since being marked as stale.

[karl-johan-grahn]

Reopening issues that inadvertently were closed as stale

[github-actions]

This issue is stale because it has been open for 60 days with no activity.

[github-actions]

This issue was closed because it has been inactive for 30 days since being marked as stale.