Add example of markdown usage in documentation

[Vamoss]

I couldn't find a dedicated page showing what formatting options are supported.

Example:

# Title
## Subtitle
### Sub-title
--- rule
*italic*
**bold**
[link text](http://url.example.com)
![image label](https://url.example.com/image.png)
<img src="https://url.example.com/image.png" width="100%" alt="image label" />
* list1
* list2

[Pyvonix]

In fact, markdown is a "normalized language" with a defined syntax (except if you decide to extend it).

By seeing the source code of markdownx you can see the following import: from markdown import markdown, who refer you Python-Markdown package. You have a great tutorial page how explains every native feature than you can use/enable. I advise you to take a look and if there is a need for further explanation don't hesitate to ask.

Maybe a line in the documentation to refer to the official Python Markdown documentation can help users?