User guide/channels guide

Channel guide with Magento integration details
You can't link to subsection of the current documentation in this way. The easiest way to achieve this, is to add a label before the headline you want to link to like this:

```rst
.. _user-guide-channels-creating-channels:

Creating a Channel
------------------
```

Please note that labels are unique across the project. That's why I chose the label this way (`user-guide` for the section, `channels` for the document, and `creating-channels` for the headline).

You can then reference to the section using the `ref` role:

```rst
You can :ref:`create <user-guide-channels-create-channels>` a specific [...]
```