util: add docs for wlr_region_scale
#include <pixman.h>
+/**
+ * Scales a region, ie. multiplies all its coordinates by `scale`.
+ *
+ * The resulting coordinates are rounded up or down so that the new region is
+ * at least as big as the original one.
+ */
void wlr_region_scale(pixman_region32_t *dst, pixman_region32_t *src,
float scale);
