improve wording

Author: vladak

intro.tex

@@ -2327,8 +2327,8 @@
 (e.g. terminals) make it possible to work with individual bytes and do not use
 buffering.
 \item \emsl{The kernel is not an individual process}, rather it is part of each
-user process. When kernel is executing, it is usually user space performing some
-action in kernel mode.
+user process. When kernel is running on a CPU, it is usually on behalf of some
+user space program performing some action in kernel mode.
 \end{itemize}