Added warning about Raspberry Pi

[Kixunil]

According to #24.

[nastevens]

In general, I'm not thrilled with the idea of having a copy-pasted warning scattered throughout the code and examples. I think a single section in the README would be a better approach, and then the code to work around the issue can be located in that one place.

I'm also not a fan of adding a hard delay to "fix" the issue. A much more robust solution would be to use something like the retry crate to try a few times with a delay between each attempt.