Set the activation hook for a plugin.

When a plugin is activated, the action ‘activate_PLUGINNAME’ hook is
called. In the name of this hook, PLUGINNAME is replaced with the name
of the plugin, including the optional subdirectory. For example, when the
plugin is located in wp-content/plugins/sampleplugin/sample.php, then
the name of this hook will become ‘activate_sampleplugin/sample.php’.

When the plugin consists of only one file and is (as by default) located at
wp-content/plugins/sample.php the name of this hook will be
‘activate_sample.php’.

function register_activation_hook( $file, $callback ) {
	$file = plugin_basename( $file );
	add_action( 'activate_' . $file, $callback );
}