Performance issues for multithreading

[ktsibikov]

Locking the thread at the moment of calling the decorated function will lead to performance degradation in the multithread setup. I think it worth mentioning the issue in the description. https://github.com/danielfm/pybreaker/blob/7f6dd0648c1bc6b5d51310d94f055aec39a1c40a/src/pybreaker.py#L213