Name of desktop file in appdir root SHOULD match?

The current section about "filesystem image" has this recommendation for the name of the desktop file in the root dir:

> - SHOULD contain exactly one $APPNAME.desktop file in its root directory with $APPNAME being the name of the payload application

This conflicts slightly with the fact that for existing applications which follow latest [xdg recommendations](https://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html#file-naming) the desktop file names these days have tld-prefixes (e.g. "org.kde.kdevelop.desktop", "org.kde.krita.desktop", "org.qt-project.qtcreator.desktop").

Also does it not match the AppDir specification at [docs.appimage.org](https://docs.appimage.org/reference/appdir.html) where it says:
> The name of the file doesn’t matter, as long as it carries the .desktop extension.

The latter is reflected also by code like from the appimagetool which picks up whatever first desktop file there is ` gchar *desktop_file = find_first_matching_file_nonrecursive(source, "*.desktop");`

So please sync the specs and extend it with some examples of applications that normally have a desktop file with a tld-prefixed name. That should help developers manually compiling appdir content to know what names are fine to use.