Minor changes to wording on how to check a background task with async_status.

Fixes #9740

Fix the example in the doc to explicitly set the poll interval to zero so the
job doesn't poll.

To run a background task without polling, you need to set the poll interval to
zero. However, Ansible's default poll setting is 15 seconds, so not specifying the poll
interval will cause a background job to poll.

Current intro doc is pointing older way of using yum module.

rules are avaialble at https://en.wikipedia.org/wiki/Wikipedia:AutoWikiBrowser/Typos

Small grammar fix

Directories need the execution bit being set therefore instead of 644, it needs 755.

Update link texts (hopefully got those correct from Sphinx documentation) and remove section on Limiting hosts as that's covered elsewhere

Ansible has modules for package managers other than yum and apt,
so update the documentation accordingly.