Added info about active users

doc/api/users.md

@@ -2,6 +2,8 @@
 
 ## List users
 
+Active users = Total accounts - Blocked users
+
 Get a list of users.
 
 This function takes pagination parameters `page` and `per_page` to restrict the list of users.
@@ -393,4 +395,4 @@ Parameters:
 - `uid` (required) - id of specified user
 - `id` (required)  - SSH key ID
 
-Will return `200 OK` on success, or `404 Not found` if either user or key cannot be found.
+Will return `200 OK` on success, or `404 Not found` if either user or key cannot be found.
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