Fix pkgdown configuration for reference

[maelle]

Some topics are missing from the configuration file.

 Error in check_missing_topics(rows, pkg) : 
  All topics must be included in reference index
• Missing topics: outfmt_get

Note that for topics you do not want to include in the index you can create an "internal" section https://pkgdown.r-lib.org/reference/build_reference.html?q=internal#missing-topics

To check all topics are listed, after editing the configuration file you can run pkgdown::check_pkgdown().

[maelle]

@ShixiangWang Friendly reminder :smile_cat:

[ShixiangWang]

@maelle Thanks for your notion. Sorry for the delay as I did not get the message before you at me. I will take a look and fix it in the two days :).

[maelle]

no problem, thank you!