request to update docs

[yaroslav-nakonechnikov]

Here: https://github.com/splunk/splunk-ansible/blob/develop/docs/advanced/default.yml.spec.md

it is not clear where to put "premium apps" for the needs of search-head cluster and other cases.

as i see, it has:
splunk.apps_location
splunk.app_paths_install.shc

and as i understand, first one for local apps only, which should be only on deployer, and second - for apps which should present on search head nodes.

but for premium apps, as they should be installed on nodes, there is no clear understanding that it should be put in splunk.apps_location.

please, update it to make documentation a bit more user-friendly.