Herobrine wasn’t added to Minecraft.
The reason the Herobrine creepypasta came in the first place was because a player in 2010 had low render distance. They saw what they thought was a player, even though the world itself was a single-player world. The player emailed Notch. I forgot what the email contained.
Anyways, that sighting is the only canon (real) sighting of Herobrine, along with the Brocraft stream (but I don’t think it’s canon. You might though).