Add help text on "Storage & Data Use" screen for iOS discrepancy

[pocketcasts]

There's a long-standing bug where iOS reports a lot more storage usage than we do. This seems to be because iOS caches some of the data we no longer need, and we have no control over that. The OS will reclaim that space if it needs it.

See Russell's Slack explanation here: p1639438147134300-slack-C02A333D8LQ

We keep getting support requests about this. It may be useful to add some help text to this screen explaining this discrepancy, so users don't have to wonder about it or question our app's credibility.

[joashrajin]

+1 @ #5530881-zen

I have deleted almost all my downloads and only have a few left. I’ve archived everything and still Podcast is taking up over 10 GB on my iPhone. Why is it taking up so much space. No matter how much I seem to delete I’m still taking up 10 GB. This is insane what’s going on

[joashrajin]

+1 at #5543942-zen

[joashrajin]

5777041-zd-woothemes

[joashrajin]

8114421-zd-a8c