Elaborate procedures due to difficulties at Hostgator to get a certificate from Let's Encrypt (cóuld be very easy, but they decided to make it difficult);
Pay Hostgator a fee at a minimum of $ 10,- (for a single domain) to install the certificate.
See Web Hosting who support Lets Encrypt for a list of (un)supported hosting providers. You can find Hostgator in the "Waiting/Delayed" section.