README: Remove 'docs' reference

On Mon, Dec 19, 2016 at 01:58:43PM -0800, Stephen Day wrote [1]:
> Just remove the part about a non-existent docs directory.

[1]: #12 (comment)

Signed-off-by: W. Trevor King <wking@tremily.us>

README.md

@@ -101,4 +101,4 @@ program, but are not ruling it out in the future.
 
 # Copyright and license
 
-Copyright © 2016 Docker, Inc. All rights reserved, except as follows. Code is released under the [Apache 2.0 license](LICENSE.code). This `README.md` file, the [`CONTRIBUTING.md`](CONTRIBUTING.md) file, and files in the `docs` folder are licensed under the Creative Commons Attribution 4.0 International License under the terms and conditions set forth in the file [`LICENSE.docs`](LICENSE.docs). You may obtain a duplicate copy of the same license, titled CC BY-SA 4.0, at http://creativecommons.org/licenses/by-sa/4.0/.
+Copyright © 2016 Docker, Inc. All rights reserved, except as follows. Code is released under the [Apache 2.0 license](LICENSE.code). This `README.md` file and the [`CONTRIBUTING.md`](CONTRIBUTING.md) file are licensed under the Creative Commons Attribution 4.0 International License under the terms and conditions set forth in the file [`LICENSE.docs`](LICENSE.docs). You may obtain a duplicate copy of the same license, titled CC BY-SA 4.0, at http://creativecommons.org/licenses/by-sa/4.0/.