Clarify how to read/write tags manually?

[leo60228]

The docs aren't very clear on how to manually read and write tags (for example, writing to a different file than originally read from, or reading/writing over the network). Based on the code, I think that something along these lines is correct:

let mut tag = Tag::read_from(&mut reader)?;
update(&mut tag);
tag.write_to(&mut writer)?;
std::io::copy(&mut reader, &mut writer)?;

However, it'd be nice if there was an example for this.