docs: update get-started

[mlmoravek]

Proposed Changes

• add vue 2 deprecation warning
• update get started section

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (13d27de) 51.93% compared to head (5e230b1) 51.93%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #699   +/-   ##
========================================
  Coverage    51.93%   51.93%           
========================================
  Files           33       33           
  Lines         1396     1396           
  Branches       515      515           
========================================
  Hits           725      725           
  Misses         671      671           

Flag	Coverage Δ
oruga-next	51.93% <ø> (ø)

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