platform: graphics: updated readme files The updated readme files are divided into several files, which makes it possible to have links from one file to another. There's more information about configuring SSH and tunneling. Finally, the information is updated to reflect the new tool capabilities. BUG=None TEST=None Change-Id: I03b12d99ca1127cbf3906b6bf618444cb3d71bda Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/graphics/+/2532769 Commit-Queue: Georges Winkenbach <[email protected]> Tested-by: Georges Winkenbach <[email protected]> Reviewed-by: Ilja H. Friedel <[email protected]> Reviewed-by: John Bates <[email protected]>