Hi all, there was a regression that I accidentally introduced into the package manager, which I have resolved now.
Apologies for the blanked list!
$ npm update nodebb-plugin-markdown // or sometimes $ npm install nodebb-plugin-markdown
Keep in mind that most plugins are kept up to date with the latest version of NodeBB, so you might also have to update your NodeBB as well, or else the plugin may not work. If you are unwilling to do so, please ask the plugin author which version is best for your version of NodeBB