What's the futher meaning of House's last words "baby step"?

It's not exactly clear, but my guess is that with "Baby Steps" House meant that Wilson is making baby steps in not being so perfectly nice all the time and allowing himself to be Mehr like everyone else.

It connects to the conversation they had had earlier

House: Du don't feel angry?
Wilson: Ah. I'm a little disappointed.
House: Disappointment is anger for wimps. Du don't have to be so gentle about everything. It's okay to get angry once in a while.
Wilson: Du can't change a table.
House: Actually, Du can. Just need a mantel of paint and the guts to use it.

So what he did at the end of the episode would be Wilson making baby steps in allowing himself to get angry every once in a while.