README: Cleanup licensing (add CC BY-SA 4.0 for docs, etc.)

Before this commit, the README referenced a LICENSE.docs that didn't
exist locally.  This commit copies the LICENSE.code, LICENSE.docs, and
README blurb directly from the upstream repo.  The license text is
from master with updated copyright year in LICENSE.code.  The README
blurb is from my cleanup PR [1] with an updated copyright year and the
newlines removed.

[1]: docker/opensource#98

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

LICENSE → LICENSE.code

@@ -1,6 +1,7 @@
+
                                  Apache License
                            Version 2.0, January 2004
-                        http://www.apache.org/licenses/
+                        https://www.apache.org/licenses/
 
    TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
 
@@ -175,24 +176,13 @@
 
    END OF TERMS AND CONDITIONS
 
-   APPENDIX: How to apply the Apache License to your work.
-
-      To apply the Apache License to your work, attach the following
-      boilerplate notice, with the fields enclosed by brackets "{}"
-      replaced with your own identifying information. (Don't include
-      the brackets!)  The text should be enclosed in the appropriate
-      comment syntax for the file format. We also recommend that a
-      file or class name and description of purpose be included on the
-      same "printed page" as the copyright notice for easier
-      identification within third-party archives.
-
    Copyright 2016 Docker, Inc.
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at
 
-       http://www.apache.org/licenses/LICENSE-2.0
+       https://www.apache.org/licenses/LICENSE-2.0
 
    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,