issue warning for documentation nodes without an example

[mahrud]

I'm looking at the package SectionRing for research and noticed a few things:

1. it would be good to issue a warning with the number of documentation nodes (at least those documenting a method) without an example, in order to encourage authors to add documentation (at the very least turn some tests into documentation examples with assertions).
2. in this package, Divisor and Varieties are imported but not exported, which has the unintended side effect that the documentation doesn't list globallyGenerated(WeilDivisor) and mRegular(CoherentSheaf) as missing documentation, but lists globallyGenerated(Ideal) and mRegular(Ideal). I think this should at least be a warning.
3. this brings me to the third strange thing, which is that the documentation installs without a single message:

2025-05-22T17:51:04.9781430Z [567/710] Installing package SectionRing
2025-05-22T17:52:06.0148170Z [568/710] Installing package ExampleSystems

There's something wrong (with the documentation system) but I'm not sure what.

[mahrud]

Also, it seems like the package documents dualToIdeal but doesn't export it, which was perhaps accidental. This should definitely be an error.