documentation: undefined anchors

[olehcambel]

Issue type:

[ ] question
[ ] bug report
[ ] feature request
[x] documentation issue

Steps to reproduce or a small repository showing the problem:

1. Open Getting started (https://typeorm.io/#/) in documentation
2. Hover the anchors and it will be marked as the examples below with undefined
   https://typeorm.io/#undefined/quick-start https://typeorm.io/#/undefined/installation
<a id="user-content-installation" class="anchor" href="#undefined/installation" aria-hidden="true">#</a>