Add Citrix Hypervisor link to integration README

[urseberry]

What does this PR do?

Adds the Citrix Hypervisor blog link to its doc page.

Motivation

Docs team Tuesday task. Improves the SEO of the blog.

Additional Notes

Review checklist (to be filled by reviewers)

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• [ ] PR title must be written as a CHANGELOG entry (see why)
• [ ] Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• [ ] PR must have changelog/ and integration/ labels attached