docs: add URL to easily consult events schema updates

Change-Id: I2133615d0b40ac3dfee40181038374116884acc0
diff --git a/docs/events_schema_updates.md b/docs/events_schema_updates.md
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+# Events schema updates
+To check whether the events schema has been updated, visit [1].
+
+[1]: https://cs.opensource.google/gerrit/gerrit/gerrit/+/master:Documentation/cmd-stream-events.txt;bpv=1