Update Template README (#12741)

* update README
remove matrix links
remove playground references (service reported as sunsetting)
OSPL rule per Docs style guide

* Apply suggestions from code review

Co-authored-by: Sacha Lansky <[email protected]>

* Update README.md

* Apply suggestions from code review

Co-authored-by: lisa-parity <[email protected]>

* (fix) chmod +x script

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Co-authored-by: Sacha Lansky <[email protected]>
Co-authored-by: lisa-parity <[email protected]>
Co-authored-by: parity-processbot <>