chore: update readme

[markphelps]

• move contribution/community sections up towards top
• remove user logos as its easier to just update on our landing page
• move contributing.md to root/update links
• add a bit more about enterprise-ready and GitOps

[github-actions]

Uffizzi Ephemeral Environment deployment-42429

☁️ https://app.uffizzi.com/github.com/flipt-io/flipt/pull/2505

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (81f4761) 70.71% compared to head (2feb14d) 70.71%.

❗ Current head 2feb14d differs from pull request most recent head 4f5a493. Consider uploading reports for the commit 4f5a493 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2505   +/-   ##
=======================================
  Coverage   70.71%   70.71%           
=======================================
  Files          81       81           
  Lines        8134     8134           
=======================================
  Hits         5752     5752           
  Misses       2035     2035           
  Partials      347      347           

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