Potential documentation updates

Since I'm going through the docs to better understand all concepts related to MongoDB and I'm quite a noob as far as the database is concerned I will describe any issues with the docs that I found in the meantime

• My first issue was this one https://github.com/spring-projects/spring-data-mongodb/issues/4760 , I tried to read more about the IndexInfo class and indexes in Mongo as such. The javadocs of IndexInfo are non existant - there's no link nor description of any of the fields such as sparse or language that are not self-explanatory. I then checked the docs about index and collection management and there was nothing there about any of the additional fields. Then I checked the Mongo DB docs about indexes and nothing was there either. Finally it was Mark who pointed me out to the subsection of the index docs in the mongo docs which I would for sure read about today (I only started yesterday). Summing it up it would be helpful to link either through the docs (preferable I guess) or javadocs to the mongo docs

Start with the IndexInfo Javadocs and the linked Spring Data MongoDB index and collection management documentation, then compare the sparse and language fields with the relevant MongoDB index documentation. Done means the non-obvious IndexInfo fields are described or linked to the appropriate MongoDB references.