docs: fix links in oras intro readme

[ganeshkumarashok]

What this PR does / why we need it:
Update links in oras introduction pages. Previous links were broken.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[codecov-commenter]

Codecov Report

Merging #1020 (963bd06) into main (5194c2e) will not change coverage.
The diff coverage is n/a.

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@@           Coverage Diff           @@
##             main    #1020   +/-   ##
=======================================
  Coverage   80.97%   80.97%           
=======================================
  Files          57       57           
  Lines        2907     2907           
=======================================
  Hits         2354     2354           
  Misses        378      378           
  Partials      175      175           

[shizhMSFT]

The issue has already been addressed by #1012

[shizhMSFT]

But... Thanks for contributing!