Update CONTRIBUTING.md

[sergiofagostinho]

Fix broken link for PlayReady docs

[opbld33]

Docs Build status updates of commit 9feefef:

✅ Validation status: passed

File	Status	Preview URL	Details
CONTRIBUTING.md	✅Succeeded

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Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

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