Document myself as a contributor.

AUTHORS.md

@@ -17,6 +17,10 @@
  * Several others made smaller contributions, which GitHub tracks here:<br>
    https://github.com/zerotier/ZeroTierOne/graphs/contributors
 
+ * Documentation additions.
+ 
+   Ben Finney <[email protected]>
+
 ## Third Party Code
 
  * LZ4 compression algorithm by Yann Collet (BSD license)<br>