doc: Address feedback about intro

src/doc/index.md

@@ -7,7 +7,7 @@
 li {list-style-type: none; }
 </style>
 
-* [A 30-minute Intro to Rust](intro.html) (read this first)
+* [A 30-minute Intro to Rust](intro.html)
 * [The Rust tutorial](tutorial.html)  (* [PDF](tutorial.pdf))
 * [The Rust reference manual](rust.html) (* [PDF](rust.pdf))
 

src/doc/intro.md

@@ -36,6 +36,9 @@ int add_one(void)
 }
 ```
 
+**Note: obviously this is very simple and non-idiomatic C++.
+You wouldn't write it in practice; it is for illustrative purposes.**
+
 This function allocates an integer on the stack,
 and stores it in a variable, `i`.
 It then returns a reference to the variable `i`.