Clarify rainbow helper.

Author: kattni

CircuitPython_Templates/status_led_one_neopixel_rainbow.py

@@ -19,9 +19,9 @@
 
 
 def rainbow(delay):
-    for j in range(255):
-        for i in range(1):
-            pixel_index = (i * 256 // 1) + j
+    for color_value in range(255):
+        for pixels in range(1):
+            pixel_index = (pixels * 256 // 1) + color_value
             pixel[i] = colorwheel(pixel_index & 255)
         pixel.show()
         time.sleep(delay)