docs/manual: Slightly improve the introduction

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

docs/manual/introduction.txt

@@ -3,11 +3,16 @@
 About Buildroot
 ===============
 
-Buildroot provides a full-featured environment for cross-development.
-Buildroot is able to generate a cross-compilation toolchain, a root
-filesystem, a Linux kernel image and a bootloader for your target.
-Buildroot can be used for any combination of these options,
-independently.
+Buildroot is a tool that simplifies and automates the process of
+building a complete Linux system for an embedded system, using
+cross-compilation.
+
+In order to achieve this, Buildroot is able to generate a
+cross-compilation toolchain, a root filesystem, a Linux kernel image
+and a bootloader for your target. Buildroot can be used for any
+combination of these options, independently (you can for example use
+an existing cross-compilation toolchain, and build only your root
+filesystem with Buildroot).
 
 Buildroot is useful mainly for people working with embedded systems.
 Embedded systems often use processors that are not the regular x86