[Feature Request] Add an option to inject html at the top of the body element

[chtixof]

In the same way that it is possible to specify a css file, I would appreciate an option to add some html code on top of the body element. On Android, I use Markor, which has this option, and I use it.
The use case for me is to add a link to the _index.md file that I keep on all my folders dedicated to Markdown.

[chtixof]

I found a trick: at the bottom of the style.css file, add:

</STYLE>
<a href="_index.md">_index.md</a><br>
<STYLE>

This does insert the HTML code, but now, the link does not work (I'd like it to open in notepad++).