Description of problem:
Docs of foreman_tasks:cleanup contain wrong information

Version-Release number of selected component (if applicable):
tfm-rubygem-foreman-tasks-0.14.4.6-1.el7sat.noarch

How reproducible:
always

Steps to Reproduce:
1. foreman-rake -D foreman_tasks:cleanup

Actual results:
rake foreman_tasks:cleanup:config
    Show the current configuration for auto-cleanup

rake foreman_tasks:cleanup:run
    Clean tasks based on filter and age. ENV variables:
    
      * TASK_SEARCH : scoped search filter (example: 'label = "Actions::Foreman::Host::ImportFacts"')
      * AFTER       : delete tasks created after *AFTER* period. Expected format is a number followed by the time unit (s,h,m,y), such as '10d' for 10 days
      * STATES      : comma separated list of task states to touch with the cleanup, by default only stopped tasks are covered, special value all can be used to clean the tasks, disregarding their states
      * NOOP        : set to "true" if the task should not actually perform the deletion
      * VERBOSE     : set to "true" for more verbose output
      * BATCH_SIZE  : the size of batches the tasks get processed in (1000 by default)
      * TASK_BACKUP : set to "true" or "false" to enable/disable task backup
    
    If none of TASK_SEARCH, BEFORE, STATES is specified, the tasks will be cleaned based
    configuration in settings


Expected results:
There should no reference shown regarding 'BEFORE' statement, as it seems this is deprecated [1]. In addition, there should be an information, that the time-value of 'started_at' will be referenced.
Also it's not really clear, how the AFTER keyword is working. 
What are the time units (s,h,m,y), when directly afterwards we talk about 'd'? If this is just an example list, it should be declared as such (like (e.g. s = seconds, h = hours, d = days, ...)

Additional info:

[1]: https://projects.theforeman.org/issues/8144