Moved app_hardware.html to app_usb.html. Will split out serial port
content into a separate article in a follow-on CL.

R=kalman@chromium.org

Review URL: https://codereview.chromium.org/34603002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230610 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230610