Add reviewers checker

This creates a new checker for the reviewers plugin and adds it to Zuul.

Change-Id: Iaa6367d6682f561291f1373639e084905a0aaf6e
diff --git a/checkers.yaml b/checkers.yaml
index 76f1423..4747ec0 100644
--- a/checkers.yaml
+++ b/checkers.yaml
@@ -100,3 +100,8 @@
     repository: "plugins/code-owners"
     name: "Zuul Check Pipeline"
     description: "Run Zuul jobs on new patchsets"
+
+  - uuid: "zuul-check:plugins_reviewers"
+    repository: "plugins/reviewers"
+    name: "Zuul Check Pipeline"
+    description: "Run Zuul jobs on new patchsets"
diff --git a/zuul/main.yaml b/zuul/main.yaml
index 7f9773e..24c54a6 100644
--- a/zuul/main.yaml
+++ b/zuul/main.yaml
@@ -33,3 +33,4 @@
           - plugins/checks
           - plugins/code-owners
           - plugins/oauth
+          - plugins/reviewers