calculus - Proof of Euler's general formula for a sum involving harmonic numbers

I have seen this formula, but how to prove this?

$$2\sum\limits_{k=1}^\infty \frac{H_k}{\left( k+1 \right)^m} =m\zeta \left( m+1 \right)-\sum\limits_{k=1}^{m-2}{\zeta \left( m-k \right)\zeta \left( k+1 \right)}$$