Add "security" to the definition of edge computing

[mtrifiro]

The LF Edge white paper included the Glossary's current definition but also added improved "security" as one of the reasons for edge computing. This needs to be propagated back into the glossary.

Here is the relevant paragraph from the white paper: "As defined in the Linux Foundation’s Open Glossary of Edge Computing, edge computing is the delivery of computing capabilities to the logical extremes of a network in order to improve the performance, security, operating cost and reliability of applications and services. By shortening the distance between devices and the cloud resources that serve them, and also reducing network hops, edge computing mitigates the latency and bandwidth constraints of today’s Internet, ushering in new classes of applications. In practical terms, this means distributing new resources and software stacks along the path between today’s centralized data centers and the increasingly large number of deployed nodes in the field, on both the service provider and user sides of the last mile network. "