Mention class format on 1-day classes

The 1-day classes are sometimes taught to people who haven’t taken
Rust Fundamentals, or who have taken it a while ago. So it seems nice
to remind everybody that questions are very welcome.

src/android.md

@@ -14,6 +14,11 @@ This course builds on [Rust Fundamentals](welcome-day-1.md) and we expect you
 are familiar with the basics of Rust. You should also be familiar with
 development on the Android Platform (AOSP).
 
+## Class Format
+
+The class is meant to be very interactive! Please ask questions to drive the
+exploration of Rust!
+
 > We will attempt to call Rust from one of your own projects today. So try to
 > find a little corner of your code base where we can move some lines of code to
 > Rust. The fewer dependencies and "exotic" types the better. Something that

src/bare-metal.md

@@ -20,3 +20,8 @@ The class is divided into several parts:
 This course builds on [Rust Fundamentals](welcome-day-1.md) and we expect you
 are familiar with the basics of Rust. You should ideally also have some
 experience with bare-metal programming in some other language such as C.
+
+## Class Format
+
+The class is meant to be very interactive! Please ask questions to drive the
+exploration of Rust!

src/chromium.md

@@ -18,3 +18,8 @@ code to connect between Rust and existing Chromium C++ code.
 This course builds on [Rust Fundamentals](welcome-day-1.md) and we expect you
 are familiar with the basics of Rust. You should also be familiar with Chromium
 development.
+
+## Class Format
+
+The class is meant to be very interactive! Please ask questions to drive the
+exploration of Rust!

src/concurrency/welcome.md

@@ -32,3 +32,8 @@ well as concepts such as:
   capture values from their environment.
 - [`Rc`](../smart-pointers/rc.md): we will use a similar type for shared
   ownership.
+
+## Class Format
+
+The class is meant to be very interactive! Please ask questions to drive the
+exploration of Rust!