Update README.md

Changed the language to be a bit stronger in recommending using the new book over the old books.

Author: Tomer-Eliahu

src/README.md

@@ -2,9 +2,8 @@
 
 Discover the world of microcontrollers through [Rust](https://www.rust-lang.org/)!
 
-There are currently three versions of this book. The first is older and uses an
-F3 Discovery circuit board to introduce you to microcontrollers and Rust, while
-the second and third are newer and use a micro:bit circuit board instead.
+There are currently three versions of this book. All of them provide an introduction to microcontrollers and how to use Rust with them. 
+Unless you need to work with a micro:bit v1 or an STM32F3 discovery board, it is *strongly* recommended that you use the latest book.
 
 - [Read the latest book, using a micro:bit v2](https://docs.rust-embedded.org/discovery-mb2/)
 - [Read the older book, using a micro:bit v1 or v2](https://docs.rust-embedded.org/discovery/microbit)