Zipreaderstream example

[jespertheend]

Fixes #509

I opted to remove the part that recompresses each file because I felt like this example is meant to focus on unzipping rather than recompressing, and this might prevent some confusion.

[gildas-lormeau]

That's fine for me. I agree that the example should stick to the essentials for greater clarity.

Thank you very much for your contribution :)