Add instructions for LICENSE file and license headers

[jhonkan]

SonarQube rules require the source files to contain the license header, but there's no instruction for that in the devguide, nor is there anything for the repo level LICENSE file.

/*!
 * Copyright (c) Trimble Inc. All rights reserved
 */

[jeffdoolittle]

That's a SonarCube thing or a general Trimble requirement? A copyright notice on every file seems like massive bureaucratic overkill to me.