Fix netsim benchmark description.

The previous description was for the old PyAuto netsim benchmark.

BUG=
NOTRY=True

Review URL: https://codereview.chromium.org/44743003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231068 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231068