pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/reference/game/change-score-by.md

@@ -0,0 +1,27 @@
+# Change Score By
+
+Add the amount you say to the score for the game.
+
+```sig
+game.addScore(1)
+```
+## Parameters
+
+* a [number](/types/number) that means how much to add to the score. A negative number means to subtract from the score.
+
+## Examples
+
+This program is a simple game.
+Press button ``A`` as much as possible.
+At the end of 10 seconds, the program will show your score.
+
+```blocks
+input.onButtonPressed(Button.A, () => {
+    game.addScore(1)
+})
+game.startCountdown(10000)
+```
+
+## See Also
+
+[score](/reference/game/score), [start countdown](/reference/game/start-countdown)