Copy docs into Zeek repo directly

This is based on commit 2731def9159247e6da8a3191783c89683363689c from the
zeek-docs repo.

doc/devel/plugins/connkey-vxlan-fivetuple-plugin-src/src/Plugin.h

@@ -0,0 +1,17 @@
+
+#pragma once
+
+#include <zeek/plugin/Plugin.h>
+
+namespace plugin {
+namespace Zeek_ConnKey_Vxlan_Vni_Fivetuple {
+
+class Plugin : public zeek::plugin::Plugin {
+protected:
+    zeek::plugin::Configuration Configure() override;
+};
+
+extern Plugin plugin;
+
+} // namespace Zeek_ConnKey_Vxlan_Vni_Fivetuple
+} // namespace plugin