go-tour: adding items to TODO

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/122230043
diff --git a/TODO b/TODO
index a11a4a8..8eb78bd 100644
--- a/TODO
+++ b/TODO
@@ -44,6 +44,7 @@
 * Range
 * Range continued
 - The blank identifier
+- Slices of slices.
 * Exercise: Slices
 * Maps
 * Map literals
@@ -59,6 +60,7 @@
 * Switch with no condition
 - Complex numbers
 * Advanced Exercise: Complex cube roots
+- the type keyword
 * Methods and Interfaces
 * Methods
 * Methods continued