docs: Explain how to enable agent debug
docs: Explain how to enable agent debug

Add details on how to enable debug for the agent process.

Fixes #1076.

Signed-off-by: James O. D. Hunt <348fbaadfbada55ea105602bf5609e23ac1c4898@intel.com>

chavafg/runtime,clearcontainers/runtime,clearcontainers/runtime,chavafg/runtime