设函数\(f(x)\)是定义在\((0 , +∞)\)上的单调函数,且对于任意正数\(x\),\(y\)均有\(f(xy)=f(x)+f(y)\),已知\(f(2)=1\),若一个各项均为正数的数列\(\{a _{n} \}\)满足\(f(S _{n} )=f(a _{n} )+f(a _{n} +1)-1(n∈N*)\),其中\(S _{n}\)是数列的前\(n\)项和,令\(b _{n} = \dfrac {1}{a_{n}a_{n+1}}\),数列\(\{b _{n} \}\)的前\(n\)项和为\(T _{n}\),则\(T _{2020}\)的值为\((\:\:\:\:)\)
A.\(2020\)
B.\( \dfrac {1}{2020}\) C.\( \dfrac {2019}{2020}\) D.\( \dfrac {2020}{2021}\)