docs: Add documenation for update command

Author: Brocco

docs/documentation/home.md

@@ -54,6 +54,7 @@ End-to-end tests are run via [Protractor](https://angular.github.io/protractor/)
 * [ng doc](doc)
 * [ng eject](eject)
 * [ng xi18n](xi18n)
+* [ng update](update)
 
 ## Angular CLI Config Schema
 * [Config Schema](angular-cli)

docs/documentation/update.md

@@ -0,0 +1,17 @@
+<!-- Links in /docs/documentation should NOT have `.md` at the end, because they end up in our wiki at release. -->
+
+# ng update
+
+## Overview
+`ng update` Updates the current application to latest versions.
+
+## Options
+<details>
+  <summary>dry-run</summary>
+  <p>
+    <code>--dry-run</code> (alias: <code>-d</code>) <em>default value: false</em>
+  </p>
+  <p>
+    Run through without making any changes. Will list all files that would have been created when running <code>ng update</code>.
+  </p>
+</details>