added example and removed redundant sct:packageDependency

[dionmcm]

• Added an example of SNOMED CT-AU as an example national extension.
• Removed redundant sct:packageDependency from the international edition example which helps clarify it is an edition as opposed to an extension package.
• Updated the Spanish edition example to include Extension in the title to help clarify it is an extension package, not an edition package.
• Added explanatory comments.