Document orientation parameter of set_attach (#6473)

doc/lua_api.txt

@@ -3392,7 +3392,7 @@ This is basically a reference to a C++ `ServerActiveObject`
* `set_attach(parent, bone, position, rotation)`
    * `bone`: string
    * `position`: `{x=num, y=num, z=num}` (relative)
    * `rotation`: `{x=num, y=num, z=num}`
    * `rotation`: `{x=num, y=num, z=num}` = Rotation on each axis, in degrees
* `get_attach()`: returns parent, bone, position, rotation or nil if it isn't attached
* `set_detach()`
* `set_bone_position(bone, position, rotation)`