update contributing.md

[yangcao77]

What does this PR do?:

update contributing.md with valid devfile doc url

Which issue(s) this PR fixes:

PR acceptance criteria:

Testing and documentation do not need to be complete in order for this PR to be approved. We just need to ensure tracking issues are opened.

• Open new test/doc issues under the devfile/api repo
• Check each criteria if:
• There is a separate tracking issue. Add the issue link under the criteria
  or
• test/doc updates are made as part of this PR
• If unchecked, explain why it's not needed

• Unit/Functional tests

• QE Integration test

• Documentation

• Client Impact

• Gosec scans

How to test changes / Special notes to the reviewer:

[codecov]

Codecov Report

Patch coverage: 67.42% and project coverage change: -0.09 ⚠️

Comparison is base (539d4b1) 60.41% compared to head (87430cc) 60.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #168      +/-   ##
==========================================
- Coverage   60.41%   60.33%   -0.09%     
==========================================
  Files          36       37       +1     
  Lines        4229     4369     +140     
==========================================
+ Hits         2555     2636      +81     
- Misses       1525     1571      +46     
- Partials      149      162      +13     

Impacted Files	Coverage Δ
pkg/devfile/parser/data/v2/header.go	100.00% <ø> (ø)
pkg/devfile/parser/data/v2/projects.go	94.73% <ø> (ø)
pkg/devfile/parser/sourceAttribute.go	85.91% <ø> (ø)
pkg/util/util.go	38.69% <ø> (ø)
pkg/devfile/generator/policy.go	64.10% <64.10%> (ø)
pkg/devfile/generator/generators.go	63.09% <69.47%> (-2.14%)	⬇️
pkg/devfile/generator/utils.go	90.90% <100.00%> (+0.28%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kim-tsao, yangcao77

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [kim-tsao,yangcao77]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment