docs(): add tooltip to back to top fab (#9806)

Closes #9805.

Author: devversion

docs/config/template/index.template.html

@@ -168,7 +168,8 @@ <h2 class="md-toolbar-item md-breadcrumb md-headline">
       <md-button class="md-fab md-fab-bottom-right docs-scroll-fab"
                  docs-scroll-class="scrolling"
                  ng-click="scrollTop()"
-                 aria-label="Jump to top">
+                 aria-label="Back to Top">
+        <md-tooltip md-direction="top">Back to Top</md-tooltip>
         <md-icon md-svg-src="img/icons/ic_arrow_up_24px.svg"></md-icon>
       </md-button>