Make all kind of limited time spawn appearance clearly notified in #game-happenings discord channel

[Zpawo]

As a not so active player, I heavily rely on discord to get notified when usually uncatchable pokemons are catchable for a limited time (I'm thinking about ursaluna bloodmoon recently but it's also true for bb greninja, ...).

I know it is announced sometime (outbreaks, ultra-beast, larvesta's form) but I would like for every kind of limited time spawn to be announced so we don't have to rely on other players telling us. I (and I'm probably not alone) missed a lot of limited time spawn not because I could not hunt at that time, but simply because I had no idea we could hunt those.