The ornamental design for a notebook, as shown and described.
FIG. 1 is a top perspective view of a notebook, showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left-side view thereof;
FIG. 5 is a right-side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof;
FIG. 8 is another top perspective view thereof; and,
FIG. 9 is a bottom perspective view thereof.
The evenly-dashed broken lines illustrating portions of the notebook form no part of the claimed design. The dot-dash broken lines in the figures represent a boundary of the claimed design and form no part of the claimed design.