Fix link to change.mergeabilityComputationBehavior in user-search.txt

According to config-gerrit.txt [1] change.indexMergeable config option
doesn't exist so it's replaced with more appropriate
mergeabilityComputationBehavior.

[1] https://gerrit.googlesource.com/gerrit/+/refs/tags/v3.4.4/Documentation/config-gerrit.txt

Release-Notes: Fix link to change.mergeabilityComputationBehavior in user-search.txt
Change-Id: Ifab3eba14b0142aaed4b2fb9276fd9355cc03c7e
diff --git a/Documentation/user-search.txt b/Documentation/user-search.txt
index ff1376b..8055f5f 100644
--- a/Documentation/user-search.txt
+++ b/Documentation/user-search.txt
@@ -497,7 +497,7 @@
 not find any abandoned but mergeable changes.
 +
 This operator only works if Gerrit indexes 'mergeable'. See
-link:config-gerrit.html#index.change.indexMergeable[indexMergeable]
+link:config-gerrit.html#change.mergeabilityComputationBehavior[change.mergeabilityComputationBehavior]
 for details.
 
 [[ignored]]