Document sinon.restoreObject()

[fearphage]

This was added recently (#2088). It needs to be documented. We could use your help.

[franck-romano]

Hi,

It will be a pleasure to contribute but I need a little help to know where to add the doc part.
Should it be located in utils.md ? :)

Thanks

[fatso83]

That seems like the right place, yes. I would also link to it from the spies and stubs sections.

If you haven't seen it, here's where to start: https://github.com/sinonjs/sinon/blob/master/docs/CONTRIBUTING.md

[franck-romano]

I've tried to make a first step by adding documentation in utils.md.
However, some tests are failing, I will look at this later if it is ok for you.