uniqueness and null could benefit from a hint for dba

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/11/indexes-unique.html
Description:

Sometimes it is convenient to create an unique index that considers NULL
values equal. Designating a "zero" value for those rows might not be
feasible, for example due to a foreign key.

The documentation currently only states that unique indexes do not consider
NULLs equal. It might be good to offer workarounds, like indexing a coalesce
function, if scans are not the reason for the index, but the uniqueness
constraint.