Undocumented behavior of headings in appendix

[bachl]

Describe the bug
If including an appendix according to the documentation, the way the headings work in the appendix is somewhat confusing and not documented.

To Reproduce
Scenario 1
If appendix.rmd (the rmd file containing the appendix) does not contain a heading, the appendix has no heading at all.

Scenario 2
If appendix.rmd (the rmd file containing the appendix) does contain headings, the appendix starts with the heading "Appendix", followed by the next heading.

Scenario 3
If one wants just the heading "Appendix" and no further headings, appendix.rmd (the rmd file containing the appendix) has to start with an empty heading, i.e. "#" and an empty line.

Expected behavior
Scenario 3 was the behavior I was looking for and it took me quite some time to figure this out. Maybe this could be included in the documentation.

Thank you for your great work with papaja!