fix visual issues

src/microbit/01.00.BUTTONS.md

@@ -6,4 +6,6 @@ The micro:bit as 3 hardware buttons, 2 user buttons and the reset button.
 
 The user buttons are wired up to be high when unpressed and low when pressed.
 
+``` rust
 {{#include examples/buttons.rs}}
+```

src/microbit/03.00.DISPLAY.md

@@ -8,4 +8,6 @@ or for monochrome images with differing brightness levels
 
 ## Blocking binary image display
 
+``` rust
 {{#include examples/display_blocking.rs}}
+```