Add explanation to VSA Days to Completion

This adds a paragraph below the "Days to completion" header on the
group-level VSA page. The intent is to explain what the chart below
represents.

doc/user/analytics/value_stream_analytics.md

@@ -339,12 +339,14 @@ Feature.disable(:value_stream_analytics_create_multiple_value_streams)
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/21631) in GitLab 12.6.
 > - [Chart median line removed](https://gitlab.com/gitlab-org/gitlab/-/issues/235455) in GitLab 13.4.
 
-This chart visually depicts the total number of days it takes for cycles to be completed.
+This chart visually depicts the total number of days it takes for cycles to be completed. (Totals are being replaced with averages in [this issue](https://gitlab.com/gitlab-org/gitlab/-/issues/262070).)
 
 This chart uses the global page filters for displaying data based on the selected
 group, projects, and timeframe. In addition, specific stages can be selected
 from within the chart itself.
 
+The chart data is limited to the last 500 items.
+
 ### Disabling chart
 
 This chart is enabled by default. If you have a self-managed instance, an

ee/app/assets/javascripts/analytics/cycle_analytics/components/duration_chart.vue

@@ -47,6 +47,13 @@ export default {
   <chart-skeleton-loader v-if="isLoading" size="md" class="gl-my-4 gl-py-4" />
   <div v-else class="gl-display-flex gl-flex-direction-column" data-testid="vsa-duration-chart">
     <h4 class="gl-mt-0">{{ s__('CycleAnalytics|Days to completion') }}</h4>
+    <p>
+      {{
+        s__(
+          'CycleAnalytics|The total time spent in the selected stage for the items that were completed on each date. Data limited to the last 500 items.',
+        )
+      }}
+    </p>
     <stage-dropdown-filter
       v-if="stages.length"
       class="gl-ml-auto"

ee/changelogs/unreleased/249803-add-explanation-for-days-to-completion.yml

+---
+title: Add description for the Value Stream Analytics Days to Completion chart
+merge_request: 43446
+author:
+type: changed

ee/spec/frontend/analytics/cycle_analytics/components/__snapshots__/duration_chart_spec.js.snap

@@ -11,6 +11,12 @@ exports[`DurationChart renders the duration chart 1`] = `
     Days to completion
   </h4>
    
+  <p>
+    
+    The total time spent in the selected stage for the items that were completed on each date. Data limited to the last 500 items.
+  
+  </p>
+   
   <stagedropdownfilter-stub
     class="gl-ml-auto"
     label="stage dropdown"

locale/gitlab.pot

@@ -8147,6 +8147,9 @@ msgstr ""
 msgid "CycleAnalytics|The given date range is larger than 180 days"
 msgstr ""
 
+msgid "CycleAnalytics|The total time spent in the selected stage for the items that were completed on each date. Data limited to the last 500 items."
+msgstr ""
+
 msgid "CycleAnalytics|Total days to completion"
 msgstr ""