Document more differences with Python: nested functions and for loops

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MOS_MIGRATED_REVID=125694309
diff --git a/site/docs/skylark/concepts.md b/site/docs/skylark/concepts.md
index 873036e..7b18012 100644
--- a/site/docs/skylark/concepts.md
+++ b/site/docs/skylark/concepts.md
@@ -176,7 +176,7 @@
 * `class` (see [`struct`](lib/globals.html#struct) function)
 * `import` (see [`load`](#loading-a-skylark-extension) statement)
 * `while`, `yield`
-* `lambda`
+* `lambda` and nested functions
 * `is` (use `==` instead)
 * `try`, `raise`, `except`, `finally` (see [`fail`](lib/globals.html#fail)
   for fatal errors).