* Update how_to_secure_network.md
Make clear that the key consists of 16 hex values and gave an example how to generate a key with command line tools.
* Clarified info about network key notation
* clarified network key notation (dec or hex)
* Update how_to_secure_network.md
Make clear that the key consists of 16 hex values and gave an example how to generate a key with command line tools.
* Remove trailing comma. #916