Fix erroneous package name in README

[skip ci]

README.md

@@ -15,7 +15,7 @@ This plugin can be installed via:
 
     python -m pip install pelican-more-categories
 
-As long as you have not explicitly added a `PLUGINS` setting to your Pelican settings file, then the newly-installed plugin should be automatically detected and enabled. Otherwise, you must add `more-categories` to your existing `PLUGINS` list. For more information, please see the [How to Use Plugins](https://docs.getpelican.com/en/latest/plugins.html#how-to-use-plugins) documentation.
+As long as you have not explicitly added a `PLUGINS` setting to your Pelican settings file, then the newly-installed plugin should be automatically detected and enabled. Otherwise, you must add `more_categories` to your existing `PLUGINS` list. For more information, please see the [How to Use Plugins](https://docs.getpelican.com/en/latest/plugins.html#how-to-use-plugins) documentation.
 
 ## Multiple Categories