Wiki for using notmuch with Emacs is outdated

[yangsheng6810 at gmail.com]

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.

-- 
Sheng Yang(杨圣), PhD student
Computer Science Department
University of Maryland, College Park
E-mail: styang at fastmail.com
E-mail(old): yangsheng6810 at gmail.com