Add clarification on log package for logging

[rogiervandenberg]

As the target audience for your overview (proficient in node, but beginner in Go) I was delighted to see all the examples. But I stumbled on an error, or so I thought 🙈

As the Logging example was omitting the timestamp in the code (as is part of the node example), I wanted to 'fix' that Logging Go example with:

fmt.Println(time.Now().Format(time.RFC3339), "hello world")

..only to find out that the log package already automagically includes the timestamp! 🎉 😮

For people moving from node to Go this is totally not obvious, so I thought it is very nice to explain that to prevent others from making the same assumption.

[miguelmota]

@rogiervandenberg Good suggestion!

Changes look good. Merging.

Thanks!