add goroutines example

[christian-korneck]

There are often questions about how to use this lib with Goroutines (i.e. #3 , DataDog#49). There's an extensive blogpost on the topic, but it's for sbinet/go-python. We should add an example (in the examples/ dir).

[esendjer]

Hi, @christian-korneck I've prepared the PR that includes that example. I also up to dated the example and tested it to be sure that it works well. Unfortunately, I'm not sure that I've done well all things about opening PR and so on. Please feel free to highlight my mistakes if they are here.

Thank you!