Missing docs in Query::par_iter and Query::par_iter_mut

[torsteingrindvik]

How can Bevy's documentation be improved?

http://dev-docs.bevyengine.org/bevy/ecs/system/struct.Query.html#method.par_iter

I'd like an example for usage of par_iter and par_iter_mut in the docs.

Several times I have reached for these APIs I keep trying to use it like so:

for transform in transforms_query.par_iter_mut()  {
    ...
});

but you have to use it like:

transforms_query.par_iter_mut().for_each(|mut t| {
    ...
});