Docs: Config page links to non-existant authentication section

Affected page: https://decapcms.org/docs/configure-decap-cms/

In the Backend section, it says "Git Gateway is an open source API that acts as a proxy between authenticated users of your site and your site repo. (We'll get to the details of that in the [Authentication section](https://decapcms.org/docs/configure-decap-cms/#authentication) below.)"

However, there is no authentication section below. The link seems to lead to an ID anchor that doesn't occur in the page.