Fix broken README.md UX guide link.

What does this MR do?

Fix the broken UX guide link in the README.md file.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

The location of the UX guide .md file was changed but the README.md was not updated to reflect that.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Marked the task Changelog entry added as completed

Marked the task Changelog entry added as incomplete

Marked the task Changelog entry added as completed

Added ~164274 ~15078 labels

Reassigned to @rymai

Status changed to merged

Mentioned in commit b8f9949a

Milestone changed to %8.15