'To add help functionality for a specific format:
In gui2.catalog.catalog_<format>.py, add the following:
from calibre.gui2 import open_url
from PyQt5.Qt import QUrl
In the PluginWidget() class, add this method:
def show_help(self):
url = \'file:///\' + P(\'catalog/help_<format>.html\')
open_url(QUrl(url))
Create the help file at resources/catalog/help_<format>.html'

def help(self):

    if ((self.tabs.count() > 1) and hasattr(self.tabs.widget(1), 'show_help')):
        try:
            self.tabs.widget(1).show_help()
        except:
            info_dialog(self, _('No    help    available'), _('No    help    available    for    this    output    format.'), show_copy_button=False, show=True)
