Generate the header for the Markdown file.

def build_header(self, title):
        """Generate the header for the Markdown file."""
        header = ['---',
                  'title: ' + title,
                  'author(s): ' + self.user,
                  'tags: ',
                  'created_at: ' + str(self.date_created),
                  'updated_at: ' + str(self.date_updated),
                  'tldr: ',
                  'thumbnail: ',
                  '---']

        self.out = header + self.out