Thank you for asking.
I don't know that it is a matter of adding index entries. They are
fairly complete as is. And the documentation is fairly complete. It's
more a matter of finding the right word search for a given need.
For my own personal needs usually a straightforward score does the job
and lilypond is great for that.
But once a week or so I'm creating scores for the same music for a group
of diverse people each with their own needs/wants. In those cases I
often find myself looking through documentation to do one specific thing
or another.
What I often find is that once I do enough google searches/asking
questions/looking through lilypond docs I find the right keyword to
search for. From there I usually find what I need - though sometimes it
take a bit of fiddling to get the syntax right.
This forum is a great help for asking questions and getting good answers.
What I have started doing for my own use when I come across something in
the reading that I may find useful currently or in the future is
creating a cheat sheet for related keywords.
For example in the case of this thread where I hadn't come across or
noticed the keyword StrokeFinger I will have a line something like below
- just enough to remind me of related keywords to search for:
Fingering
FIngering_Engraver (can be applied to TabVoice)
New_Fingering_Engraver (can be applied to TabVoice)
rightHandFinger
StrokeFinger