Add "alterable_logger" link to README.md

[brummer-simon]

Hi,

I wrote a utility crate for log. To promote it, I though it is a good Idea to add a link to the log README file. Here is the corresponding PR.

Cheers Simon

[Thomasdezeeuw]

@brummer-simon can you rebase, then we can merge this.

[brummer-simon]

Done

[Thomasdezeeuw]

Thanks @brummer-simon