Update all_clusters_app README (#14863)
Update all_clusters_app README (#14863)

The instructions currently customize the device via menuconfig.
This bypasses the various customizations from the device specific
defaults.

Add a section to encourage users to start with the device specific
defaults to avoid running into hard to debug run-time issues.
project-chip/connectedhomeip,nestlabs/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,nestlabs/connectedhomeip,nestlabs/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,project-chip/connectedhomeip