Update documentation to point to Rake task to deduplicate tags
What does this MR do?
This MR accompanies gitlab!181280 (merged) to document the move of the gitlab$3700665 snippet to a proper official rake task.
Why was this MR needed?
So that users know to use the new Rake task instead of the unmaintained snippet.
What's the best way to test this MR?
What are the relevant issue numbers?
Edited by Pedro Pombeiro