Add a "who's using freeze-dry" section to readme

[pataquets]

Found this lib while googling for an end-user tool. Although I'm no JS/TS developer who can benefit from it, I could use a list of tools using this lib. It would also give more visibility of the library itself, apart from the depending software.
Just adding a section with a few known users would suffice, hoping for others using it to add themselves to the list with a simple PR.

[Treora]

Thanks for the suggestion, will keep this in mind. But as far as I know none of the current users of freeze-dry are using it in production-ready end-user tools for web page snapshotting.

Note that Github does attempt to generate a list of Github-hosted projects that depend on it, which may give somewhat of an idea already: https://github.com/WebMemex/freeze-dry/network/dependents

It is however used in (and spun off from) the WebMemex browser extension, but you likely saw that already.