[reclient] Update reclient_metrics.README.md to reflect that we collect googler hostnames

This was approved in the PDD for reclient metrics

Bug: b/290921206
Change-Id: Ib9a38f1143d3a05e76ce75fc4bc6e9299d4dafb4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4705043
Reviewed-by: Andy Perelson <ajp@google.com>
Auto-Submit: Ben Segall <bentekkie@google.com>
Commit-Queue: Ben Segall <bentekkie@google.com>

reclient_metrics.README.md

@@ -53,7 +53,9 @@ This contains
 * OS (e.g. Win, Mac or Linux)
 * Number of cpu cores and the amount of RAM of the building machine
 
-We don't collect personally identifiable information
+
+We collect googler hostnames to help diagnose long tail issues.
+We don't collect any other personally identifiable information
 (e.g. username, ip address).
 
 ## Why are reproxy metrics collected? / How are the metrics collected?