Copy docs into Zeek repo directly

This is based on commit 99e6942efec5feff50523f6b2a1f5868f19ab638 from the
zeek-docs repo.

doc/devel/plugins/event-metadata-plugin-src/scripts/__load__.zeek

@@ -0,0 +1,11 @@
+module EventLatency;
+
+redef enum EventMetadata::ID += {
+	## Identifier for the absolute time at which Zeek published this event.
+	WALLCLOCK_TIMESTAMP = 10001000,
+};
+
+event zeek_init()
+	{
+	assert EventMetadata::register(WALLCLOCK_TIMESTAMP, time);
+	}