Add Gerrit Config for number of relevant changes to suggest reviewers

Currently, we go over 25 of the most recent changes of the user and give
priority to users that are reviewers of any of those changes.
This change allows user to configure how many changes are relevant,
and how many of those changes we should actually go over. Also, default
increased to 50.

Change-Id: Ie8370684093e822e998c91d89b4f7d08f6810eb2

Documentation/config-gerrit.txt

diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index 880626e..6968e83 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -4784,6 +4784,15 @@
 used for suggesting accounts when adding members to a group.
 +
 By default 0.
+[[suggest.relevantChanges]]suggest.relevantChanges::
++
+When suggesting reviewers, we go over recent changes of the user, and
+give priority to users that are present as reviewers in any of those
+changes. The number of changes we go over is `sugggest.relevantChanges`.
++
+By default 50. This nubmer is a tradeoff between speed and accuracy.
+A high number would be accurate but slow, and a low number would be
+fast but inaccurate.
 
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 === Section tracing