Reservoir computing (RC) has been considered as one of the key computational principles beyond von-Neumann computing. Magnetic skyrmions, topological particle-like spin textures in magnetic thin films, are particularly promising for implementing RC 1 since they respond strongly nonlinear to external stimuli and feature inherent multiscale dynamics. We propose and demonstrate experimentally a conceptually new approach to skyrmion RC that exploits the thermally activated diffusive motion of skyrmions 2. By confining the thermal and low-energy, electrically gated skyrmion motion, together with employing spatially resolved input and readout, we find that already a single skyrmion in a confined, triangular geometry (Fig. 1) suffices to realize non-linearly separable functions, which we demonstrate for the XOR gate along with all other Boolean logic gate operations 3 (Fig. 2). Our proposed concept can be readily extended by linking multiple confined geometries and/or by including more skyrmions in the reservoir, suggesting high potential for scalable and low-energy reservoir computing.