Add collator selection tool tips (#900)

* First doc lines should show as tool tips

* Update pallets/collator-selection/src/lib.rs

* Update pallets/collator-selection/src/lib.rs

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update pallets/collator-selection/src/lib.rs

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Update pallets/collator-selection/src/lib.rs

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* moving comment onto storage

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>