Thank you, David. I just added notes about it. Hope this can save time for other confused users like me.

On Fri, Sep 13, 2019, at 8:42 PM, David Bremner wrote:
> yangsheng6810@gmail.com writes:
> 
> > The package name for `org-notmuch.el` was changed to `ol-notmuch` in the following commit in org-mode on March 2nd 2019.
> >
> > 499c0a50c * bad Prefix link-related libraries filenames with "ol"
> >
> > Therefore, the descriptions at https://notmuchmail.org/emacstips/#index24h2 need to be updated.
> >
> 
> I guess it depends on version of org. I'm still running org-mode 9.2.3,
> and the old name is present there.
> 
> In any case, feel free to add some notes about the changes in more
> recent versions of org-mode; see [1] for how.
> 
> [1]: https://notmuchmail.org/wikiwriteaccess/
>