Add documentation about the uploaded recordings

In our Matrix channel smaug said:
> The page just says "Recent uploaded recordings". I don't know if those are mine or someone elses

It looks like it's not very clear who these recordings belong to. Also it's not clear how we are storing this data in the browser right now (spoilers: indexed db). [We have a section](https://profiler.firefox.com/docs/#/./guide-getting-started?id=delete-an-uploaded-profile) about deleting the profile data in our docs already. I think we can expland this section a bit more and explain these as well.
Also we can add a "i" button on the right side of this "recent uploaded recordings" section that links to this doc.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-568)