polygerrit-ui: add a tooltip for 'Updated' metadata field

This lets us simplify the UI Documentation.

Change-Id: I803fe30813ba51a91e8e612c048286a7abd52bfa

polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.ts

diff --git a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.ts b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.ts
index 8c8a886..ed38d6f 100644
--- a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.ts
@@ -153,7 +153,14 @@
     <section
       class$="[[_computeDisplayState(_showAllSections, change, _SECTION.UPDATED)]]"
     >
-      <span class="title">Updated</span>
+      <span class="title">
+        <gr-tooltip-content
+          has-tooltip=""
+          title="Last update of (meta)data for this change."
+        >
+          Updated
+        </gr-tooltip-content>
+      </span>
       <span class="value">
         <gr-date-formatter
           has-tooltip=""