releasing key guide under CC 4.0 BY-SA

_ref/KEY_GUIDE.adoc

@@ -15,6 +15,12 @@ Last updated {localdatetime}
 :source-highlighter: rouge
 :docinfo: shared
 
+////
+This work is licensed under the Creative Commons Attribution-ShareAlike 4.0 International License.
+To view a copy of this license, visit
+http://creativecommons.org/licenses/by-sa/4.0/.
+////
+
 == Purpose
 This document attempts to present a much more detailed, thorough, and easily-understood form of the key formats used by OpenSSH. The extent of those formats' canonical documentation is https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.key[the OpenSSH source tree's `PROTOCOL.key`^], which is a little lacking.
 
@@ -62,3 +68,15 @@ All public keys in v1 continue to use the same packed binary format as <<public_
 include::rsa/main.adoc[]
 
 include::ed25519/main.adoc[]
+
+== Further Information
+
+++++
+<a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">
+	<img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by-sa/4.0/88x31.png" />
+</a><br />
+<span xmlns:dct="http://purl.org/dc/terms/" href="http://purl.org/dc/dcmitype/Text" property="dct:title" rel="dct:type">OpenSSH Key Structure Guide</span> by <a xmlns:cc="http://creativecommons.org/ns#" href="https://r00t2.io/" property="cc:attributionName" rel="cc:attributionURL">Brent Saner</a> is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International License</a>.<br />
+<br />
+++++
+
+You are free to use, distribute, modify, redistribute, use for commercial purposes, etc. with very few restrictions; please see http://creativecommons.org/licenses/by-sa/4.0/[the license summary^] and https://creativecommons.org/licenses/by-sa/4.0/legalcode[full license^] for further details.