Increase header level on included markdown

[ElinoraWhite]

The keyword Include can be used to incorporate markdown fragments stored as separate files into the document. Included files may include section headers.

PSDocs allows defining section headers that are structured hierarchically and the header level is automatically selected.

Included files are treated as raw input and do not follow the same structure.

Instead, header levels in included files should be automatically updated to align to hierarchical pattern, relative to their position in the document.