The online installation instructions:
Download the plugin file
Unzip the file into a folder on your hard drive
Upload /add-new-users/ folder to /wp-content/plugins/ folder on your site
Visit Network Admin -> Plugins and Network Activate it there.
Note: If you have an older version of the plugin installed in /mu-plugins/ please delete it.
There is no “add-new-users” folder. The “add-new-users.php”
The installation.txt file instructions:
add-new-users.php – goes in /wp-content/mu-plugins
1) Place the files in the specified directories