Add nested summaries for newer courses (#2425)

docs/courses/blocks-to-javascript/SUMMARY.md

@@ -0,0 +1,8 @@
+# [Blocks to JavaScript](/courses/blocks-to-javascript)
+
+* [Blocks to JavaScript](/courses/blocks-to-javascript)
+    * [Hello JavaScript](/courses/blocks-to-javascript/hello-javascript)
+    * [Starter Blocks](/courses/blocks-to-javascript/starter-blocks)
+    * [Writing Code](/courses/blocks-to-javascript/writing-code)
+    * [Conditional Loops](/courses/blocks-to-javascript/conditional-loops)
+    * [Writing Functions](/courses/blocks-to-javascript/writing-functions)