Specify that update via ref-update is only for primaries

Change-Id: I702423cb0d09d2b710a284cd077afb04b0aa93fc

README.md

diff --git a/README.md b/README.md
index 987d373..10a5aa8 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,8 @@
 with Gerrit, however it's possible for it to work with multiple Git SCM systems, including bare
 Git repositories.
 
-Metrics are updated upon a `ref-update` receive.
+Metrics are updated either upon a `ref-update` receive or on a time based refresh interval.
+`ref-update` events are received only on primary nodes, so on replicas `gracePeriod` will need to be set.
 
 ## How to build
 

src/resources/Documentation/config.md

diff --git a/src/resources/Documentation/config.md b/src/resources/Documentation/config.md
index 28e2aa7..e2e08d0 100644
--- a/src/resources/Documentation/config.md
+++ b/src/resources/Documentation/config.md
@@ -2,7 +2,8 @@
 ======================
 
 The @PLUGIN@ allows a systematic collection of repository metrics.
-Metrics are updated upon a `ref-update` receive.
+Metrics are updated either upon a `ref-update` receive or on a time based refresh interval.
+`ref-update` events are received only on primary nodes, so on replicas `gracePeriod` will need to be set.
 
 Currently, the metrics exposed are the following:
 
@@ -56,4 +57,3 @@
 Currently supported values:
 - GERRIT (default)
 - GITLAB
-