Suggest change in documentation for numeric mapping entries

[brahmafear]

The documentation does not mention that the mac_address_X mapping entries must be in consecutive numeric order (after the first 25). This caused me some confusion as I assumed that the numeric part of the key simply needed to be unique and created the numeric based on the device's IP last octet.

Suggest mentioning in the documentation that numerics should be in increasing, consecutive order starting with 1.