$\large \sqrt{\dfrac{x+y}{x+y+z}}+ \sqrt{\dfrac{y+z}{x+y+z}}+ \sqrt{\dfrac{z+x}{x+y+z}}$

Once, Calvin was learning inequalities and he came across the above expression where $x,y,z$ are positive real numbers. Calvin maximized it and obtained the maximum value of the expression above as $M$. Calculate $M$ correct to 2 decimal places.