Document spawn outdoors attribute

[TheRealPear]

https://github.com/search?q=repo%3APGMDev%2FPGM%20outdoors&type=code

This attribute will make a player spawn at the highest point of a spawn region. For example, this could be used to stop players from getting stuck in a hollowed out map with a large, generalized spawn.

[Pablete1234]

Not the highest point of a region, the highest point of the world (ie: the highest block in the world at that x,z).

In other words: it won't allow spawning in a position unless such position is above the highest block in the world in that x,z position.