Update README.md

[Allanbikundo]

Hello there

So rotating-file-stream now needs one to call the function createStream to work

[diglopes]

After v2 there is no default export, you need to call "createStream" method.

[jonchurch]

Closes #217

[dougwilson]

This keeps popping up, and in the interim there is some confusion. Can we add to the example the specific version of the rotating-file-stream the example represents?

[a10kiloham]

+1 - please push this README change; it just happened to me and had to google to get here :)

[dougwilson]

I'm just waiting for the requested change to be made from the review comment. If I don't hear back in a week or so I will make the change myself instead, but then OP will loose credit on it, so wanted to give a chance.

[ryhinchey]

@Allanbikundo thank for this PR! There's a request here to update the docs to reference the version of rfs that doesn't have a default export. Here's the rfs v1 > v2 upgrade docs: https://github.com/iccicci/rotating-file-stream#upgrading-from-v1xx-to-v2xx

Is this a change you can make? That seems to be the only thing left to get this PR in.