documentation: Traffic Capture methods

documentation: Traffic Capture methods

Created new chapter on Traffic Capture and added short descriptions and explanation for each of the three methods currently supported by VSPERF. Subchapters include Traffic Capture in the VM, Traffic for testing NICs with Hardware acceleration and Traffic Capture on the Trraffic Generator.

JIRA: VSPERF-556

Change-Id: I280c54aa73961e0bbb61b40e8fe476bd3e92ff7d
Signed-off-by: Richard Elias <richardx.elias@intel.com>
Reviewed-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>
Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>