fixes and updates to inventory intro (#2416)

* fixes and updates to inventory intro

* Apply suggestions from code review

Co-authored-by: Abhijeet Kasurde <[email protected]>

* fix typo

* fix vars plugin refs

* example

* Update docs/docsite/rst/inventory_guide/intro_inventory.rst

Co-authored-by: Abhijeet Kasurde <[email protected]>

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Co-authored-by: Abhijeet Kasurde <[email protected]>

Author: bcoca