WP-CLI Description should be meaningful

[jessecowens]

The current output of wp help lists the class name of the various commands, rather than a human-readable string describing the purpose of the command. Other commands use a brief description of the purpose of the command.

Replcation:
Execute wp help

Expected behavior:
Instead of "Class: W3TotalCache_Command," the description should read something like "Manage W3TC settings, flush, and prime the cache"