[Docs] Document the use of meta methods for client.playerList

[Seniru]

https://github.com/Lautenschlager-id/Transfromage/blob/cb699b5bea9c157f1f1f2c46178b49af8f3918ef/libs/client.lua#L111

According to libs/client.lua#L111, the field playerList is associated with a meta table which defines the meta methods __len and __pairs, which of course allows us to do operations like #client.playerList and pairs(client.playerList)

But as far as I can see, those meta methods are not documented

In my opinion it would be easier for both users and developers if they are documented