Fix pixel / bitmap order in README.md

Avoid buffer overflow

micropython/modules/pico_scroll/README.md

@@ -88,7 +88,7 @@ picoscroll.set_pixels(image)
 ### show_bitmap_1d
 
 Show a view of a bitmap stored as the 7 least significant bits of
-bytes in a `bytearray`, top-down. Individual pixels are set to
+bytes in a `bytearray`, bottom-up. Individual pixels are set to
 `brightness` based on individual bit values, with the view defined by
 the offset and the width of the scroll (i.e. 17 columns). Changes will
 not be visible until `update()` is called.

micropython/modules/pico_scroll/pico_scroll.cpp

@@ -111,7 +111,7 @@ mp_obj_t picoscroll_show_bitmap_1d(mp_obj_t bitmap_obj, mp_obj_t brightness_obj,
 
 	for (int x = 0; x < width; x++) {
 	    int k = offset + x;
-	    if ((k >= 0) && (k <= length)) {
+	    if ((k >= 0) && (k < length)) {
 	        unsigned char col = values[k];
 		for (int y = 0; y < height; y++) {
 		    int val = brightness * ((col >> y) & 1);