User guide still says Stan doesn't support MAP estimate

[jgabry]

Summary:

Stan supports MAP estimation now so this part of the doc on clustering should be updated:

https://github.com/stan-dev/docs/blob/cc4a208700cbb76bb4bea79f75b0513ff26c3d7d/src/stan-users-guide/clustering.Rmd#L559-L560

Current Version:

v2.33.0

[jgabry]

@bob-carpenter This is in the section you wrote about correlated topic models. I could just fix this sentence, or do you want to update this section more than that now that Stan supports MAP estimation?

[avehtari]

Pinging @bob-carpenter who asked to point out doc issues he could work on in the near future