In the beta UI, it provides hard coded links to the last test build... which are unusable in a README (because that would trigger a new build, making the just committed url stale).
The https://saucelabs.com/u/SAUCE_USERNAME view that actually can be used in a README, doesn't have the great new style of the beta UI. and shows too much build history
I think during development, there's likely to be a number of builds that fail... which isn't exactly what you want to advertise when someone looks for more details in the current passing build... especially considering it won't say why they failed, and the whole point of testing is to inspire developer confidence.
Ideally, when navigating to https://saucelabs.com/u/SAUCE_USERNAME, (The current build matrix for embedding in READMEs) I would see a view focused on the latest build, with more information available if you click deeper. This would be in the same style as the Build screen seen when logged in, and 'drilling down' would show test details.