Feature to inject HTML

[chtixof]

Hello. I would appreciate a feature to inject HTML at top of the BODY and also at the bottom of the HEAD.
That would allow me to add a link on top to display the folder contents and another one to display an index.md (or a README.md) file.
In the meantime, is there an alternative solution to reach this result, using another software or hack.
Thanks and congrats for your extension.
PS: For your information, in parallel, on mobile, I use the application Markor that has this feature (in the settings/view mode) and I am glad to use it.