Display number of shown events on Plan stage of Cycle Analytics

app/assets/javascripts/cycle_analytics/components/stage_plan_component.js.es6

@@ -13,6 +13,11 @@
       <div>
         <div class="events-description">
           {{ stage.description }}
+          <span class="pull-right has-tooltip"
+                title="Limited to a maximum of 50 events"
+                data-placement="top">
+            Showing {{ items.length }} events
+          </span>
         </div>
         <ul class="stage-event-list">
           <li v-for="commit in items" class="stage-event-item">

app/assets/stylesheets/pages/cycle_analytics.scss

@@ -284,7 +284,11 @@
 
     .events-description {
       line-height: 65px;
-      padding-left: $gl-padding;
+      padding: 0 $gl-padding;
+
+      span {
+        color: $gl-text-color-secondary;
+      }
     }
   }