labs/sysdev-tinysystem: further improve Busybox build explanations

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

Author: tpetazzoni

labs/sysdev-tinysystem/sysdev-tinysystem.tex

@@ -194,9 +194,15 @@ \section{Root filesystem with BusyBox}
 \end{bashinput}
 
 Prior to building Busybox, make sure your \code{CROSS_COMPILE}
-environment is set to the correct value.
+environment is set to the correct value, pointing to the toolchain we
+have previously compiled, and used to build our bootloader and Linux
+kernel.
 
-Build BusyBox using the toolchain that you used to build the kernel.
+Build BusyBox:
+
+\begin{bashinput}
+$ make
+\end{bashinput}
 
 Going back to the BusyBox configuration interface,
 check the installation directory for BusyBox\footnote{You will find