Trouble adding custom CiviRule action
In Create your own action you find a description for extending CiviRules with a custom action. The example action SoftDelete has the class CRM_CivirulesActions_Contact_SoftDelete should be placed in the file
 ../ext/org.civicoop.civirules/CRM/CivirulesActions/Contact/SoftDelete.php

It is also possible to add a custom action to your own extension. An example of such an extension can be found at https://github.com/CiviCooP/org.civicoop.wpcivirules . (But be aware old versions of CiviRules worked with managed entities (*.mgd.php) files. This still works but the latest version works with direct sql statements).