This ETF has outpaced the S&P 500 over the past five years.There are many good reasons to invest in small-cap stocks, such as their potential for faster growth -- and the potential for them to be bought out at a premium by bigger companies.If you're looking to add some to your portfolio, you might want to consider this solid exchange-traded fund (ETF) that's focused on small-cap stocks: the Avantis U.S. Small Cap Value ETF (AVUV -0.03%).Here's an introduction to it, its performance record, and its holdings. ...