Add speaker notes to flow control basics (#2498)

Part of #1083.

src/control-flow-basics.md

@@ -1,3 +1,12 @@
 # Control Flow Basics
 
 {{%segment outline}}
+
+<details>
+
+- We will now cover the many kinds of flow control found in Rust.
+
+- Most of this will be very familiar to what you have seen in other programming
+  languages.
+
+</details>

src/control-flow-basics/loops/loop.md

@@ -15,3 +15,10 @@ fn main() {
     }
 }
 ```
+
+<details>
+
+- The `loop` statement works like a `while true` loop. Use it for things like
+  servers which will serve connections forever.
+
+</details>