[Speed] Update run-speed-test.mdx (#25531)

Hello team,

Can we refer to docs on RUM here?

https://developers.cloudflare.com/speed/observatory/#real-user-monitoring-rum

Thanks!

Author: nenizera

src/content/docs/speed/observatory/run-speed-test.mdx

@@ -30,7 +30,7 @@ In the Tested URLs table, in the last column, you can select the three dots > **
 
 ## Enable real user monitoring (RUM)
 
-Once a test has been run, you can enable RUM data in the test results page:
+Once a test has been run, you can enable [RUM](/speed/observatory/#real-user-monitoring-rum) data in the test results page:
 
 1. Go to **Observatory** and select **Enable RUM**. You can choose to enable globally or enable everywhere except the EU.
 2. Once RUM data is running on your site, you can access **Real user measurements** on your test results page. Usually it takes less than five minutes to see the data coming in, but it will depend on traffic.