Show code comment syntax and basic data types before moving on

Author: José Valim

README.md

@@ -40,6 +40,18 @@ iex> 40 + 2
 42
 iex> "hello" <> " world"
 "hello world"
+iex> # This is a code comment
+nil
+```
+
+Besides numbers and strings above, we also use frequently the following data types:
+
+```iex
+iex> :atom           # An identifier (known as Symbols in other languages)
+:atom
+iex> [1, 2, "three"] # Lists (can hold any item)
+[1, 2, "three"]
+iex> {:ok, "value"}  # Tuples (can hold any item)
 ```
 
 Once we finish our portal application, we expect to be able to type the following code inside `iex`: