add js libraries and css files of mermaid js_file

def _add_mermaid_js(self):
        """add js libraries and css files of mermaid js_file"""
        self.add_javascripts('{}/js/jquery-1.11.3.min.js'.format(self.resources_path))
        self.add_javascripts('{}/js/mermaid.min.js'.format(self.resources_path))
        self.add_stylesheets('{}/css/mermaid.css'.format(self.resources_path))
        self.main_soup.script.append('mermaid.initialize({startOnLoad:true  });')