put lessons back for Michael

docs/lessons/snowflake-fall/challenges.md

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+# snowflake fall blocks challenges
+
+Coding challenges for snowflake fall. 
+
+## Before we get started
+
+Complete the [snowflake fall](/lessons/snowflake-fall/activity) activity and your code will look like this:
+
+```blocks
+basic.forever(() => {
+    basic.showLeds(`
+        . . . . .
+        . . # . .
+        . # # # .
+        . . # . .
+        . . . . .
+        `)
+    basic.showLeds(`
+        . . # . .
+        . # . # .
+        # . . . #
+        . # . # .
+        . . # . .
+        `)
+})
+```
+
+### Challenge 1
+
+
+
+To finalize our snowflake fall, let's add a different snowflake pattern.
+
+```blocks
+
+basic.forever(() => {
+    basic.showLeds(`
+        . . . . .
+        . . # . .
+        . # # # .
+        . . # . .
+        . . . . .
+        `)
+    basic.showLeds(`
+        . . # . .
+        . # . # .
+        # . . . #
+        . # . # .
+        . . # . .
+        `)
+    basic.showLeds(`
+        . # . # .
+        # # # # #
+        . # . # .
+        # # # # #
+        . # . # .
+        `)
+})
+
+```
+
+
+* Run your program and see if it works.
+
+### Challenge 3
+
+Add a fourth frame to the current animation... or make it your own!
+