DOC-548: remove duplicate info, add xref to readme

[amandalindsay]

As part of the docs work to move technical content such as install & getting started info into the docs site, this is to remove the duplicate information and add a link to the docs site instead.
See doc ticket: https://hazelcast.atlassian.net/browse/DOC-548

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.43%. Comparing base (ef8f568) to head (8eaab7f).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1537      +/-   ##
==========================================
- Coverage   93.45%   93.43%   -0.02%     
==========================================
  Files         466      466              
  Lines       16628    16628              
  Branches     1350     1350              
==========================================
- Hits        15540    15537       -3     
  Misses        797      797              
- Partials      291      294       +3     

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