image: add documentation for view

src/image.zig

@@ -75,6 +75,8 @@ pub fn Image(comptime T: type) type {
             return self.rows == other.rows and self.cols == other.cols and self.data.len == other.data.len;
         }
 
+        /// Returns an image view with boundaries defined by `rect`.  The returned image
+        /// references the memory of `self`, so there are no allocations or copies.
         pub fn view(self: Self, rect: Rectangle(usize)) Image(T) {
             assert(rect.r < self.cols);
             assert(rect.b < self.rows);