Custom WordPress Plugins
It seems that the wordpress plugin page lists those plugins held in the ./wp-content/plugins folder.
The article, What, Why, and How-To’s of Creating a Site-Specific WordPress Plugin shows how to create a container. They advise that it is located in its own directory. Doing this creates an entry in a the Plugins, installed plugins page on the dashboard.
This page at stackoverflow documents how to put a posts tag list into the article.
And this is wordpress’s documentation on the Read More functions.