HierarchicalQueue docs don't explain deserved/guarantee behavior when unset #542

The HierarchicalQueue page (docs/KeyFeatures/HierarchicalQueue.md) explains what happens to capability when a queue does not set it: it inherits up the tree, ultimately from the root queue's cluster-total default. But it does not say anything about deserved/guarantee when they are unset.

This came up in volcano-sh/volcano#5634. As @hajnalmt explained there, deserved and guarantee are lower bounded (unset means 0) while capability is upper bounded (unset means infinity/inherited), so a child queue cannot set deserved/guarantee if its parent does not. The page currently only says the sum of children cannot exceed the parent, which leaves this part unclear.

I would like to reword that section so the lower-bound (deserved/guarantee) vs upper-bound (capability) behavior is spelled out. Happy to send a PR.