Walgreens Boots Alliance's (WBA 0.17%) stores dot the U.S. landscape, given that it is one of the largest pharmacy retailers in the country. But as an investment, well, it hasn't performed very well for a little while. And now it is heading into private hands. Here are three things you need to know before you buy Walgreens stock today.1. Walgreens has been strugglingThe most important thing to keep in mind when you look at Walgreens today is -- unfortunately-- its weak business performance. It really isn't ...