Add or update custom tags

Tag an entity with your own tags, custom sector, custom entity type, and notes. Tags are merged into /follows/enriched and /classify responses and matched by the tag filter. Upserts on the entity, so repeat calls update the record. Identify the entity by twitter_user_id or username (username is resolved via the classification cache and returns 404 if unknown). Free, costs 0 credits. Limit 10,000 tagged entities (100,000 on Enterprise).