put lessons back for Michael

docs/lessons/counter/challenges.md

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+# counter challenges
+
+Coding challenges for the counter.
+
+## Before we get started
+
+Complete the following [guided tutorial](/lessons/counter/activity) At the end of the tutorial, click **keep editing**. Your code should look like this:
+
+```blocks
+let count = 0
+input.onButtonPressed(Button.A, () => {
+    count = count + 1
+    basic.showNumber(count)
+})
+```
+
+### Challenge 1
+
+Let's add the code to `count` when `B` is pressed. Add an event handler with `on button pressed(B)` then add the code to `count`.
+
+
+```blocks
+let count = 0
+input.onButtonPressed(Button.A, () => {
+    count = count + 1
+    basic.showNumber(count)
+})
+input.onButtonPressed(Button.B, () => {
+    count = count - 1
+    basic.showNumber(count)
+})
+```
+
+### Challenge 3
+
+Now let's try to reset the counter when the micro:bit is shaken. You will need to register an event handler with `on shake`.
+