chore: fix doc repo URL in PR template

[avishnu]

Pull Request template

Please, go through these steps before you submit a PR.

Why is this PR required? What issue does it fix?:
Incorrect doc repo URL in the PR template

What this PR does?:
Fixes the URL

Does this PR require any upgrade changes?:
No

If the changes in this PR are manually verified, list down the scenarios covered::

Any additional information for your reviewer? :
Mention if this PR is part of any design or a continuation of previous PRs

Checklist:

• Fixes Incorrect documentation repo URL in the PR template #544
• PR Title follows the convention of <type>(<scope>): <subject>
• Has the change log section been updated?
• Commit has unit tests
• Commit has integration tests
• (Optional) Are upgrade changes included in this PR? If not, mention the issue/PR to track:
• (Optional) If documentation changes are required, which issue on https://github.com/openebs/openebs-docs is used to track them:
• subject is a single line brief description of the changes made in the pull request.