Some teams keep their documentation along with source code, and require every pull request to update both code and documentation. The job of the person doing the PR review is to verify that code and docs are in sync.
The documentation in code has a few problems. People using this method usually only keep the documentation related to engineering in their code repository.
We believe documentation review should happen by the product and testing team as well. Assigning the job of code review to product managers or testing team is not feasible, and does not happen. End result is documentation is too biased and limited towards engineering aspects, and how does the product work is missing. Which means a new developer who joins still does not know how the product works overall and has to take sessions with product manager etc to understand how it works etc.