Updated README.txt to README.md

Pracheth S Prequested to merge
issue/extrafield_views_integration-3319925:3319925-replace-readme.txt-with into 2.x

Updated README.txt to README.md. Also reviewed the patch(3319925-6.patch) by komalparmar, The patch didn't apply cleanly, Had errors. Screenshot_2022-11-13_081145 Also updated the Markdown render for code block as per the Drupal Markdown practices and addressed the pointers by abramm #4. Please review the same.

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