How to get the Rockspine Basilisk mount (World of Warcraft: Legion)

The Rockspine Basilisk is a new mount added in patch 7.1 of World of Warcraft.However, it's not obtainable in patch 7.1, but will be in patch 7.1.5. This mount is tied to the Legion Brawler's Guild, and the exact source is not known, however it seems likely that it is rewarded upon reaching a certain rank with the guild.