Why has David Tong in his Standard Model Lectures a global minus sign in front of the Dirac action?
$$S_\mathrm{Dirac}=-\int\mathrm{d}^4x(\operatorname{i}\bar{\psi}\gamma^\mu\partial_\mu\psi-M\bar{\psi}\psi)$$
This convention is also used on page 186 when he couples the fermions to the gauge fields.
