Merge pull request #186 from buildpacks/non-root

Add initial non-root requirement documentation

docs/reference/spec/platform-api/index.html

@@ -338,6 +338,8 @@ <h2 id="buildpacks">Buildpacks</h2>
 <li>Each top-level directory is a buildpack ID.</li>
 <li>Each second-level directory is a buildpack version.</li>
 </ul>
+<h2 id="users">Users</h2>
+<p>For security reasons, images built with platforms, such as <code>pack</code>, build and run as non-root users.</p>
 <h2 id="further-reading">Further Reading</h2>
 <p>You can read the complete <a href="https://github.com/buildpacks/spec/blob/main/platform.md">Platform API specification on Github</a>.</p>