fix wording

Author: vladak

threads.tex

@@ -1144,8 +1144,8 @@
 the thread is woken up, the system will lock the mutex first (this will be done
 by the condition variable implementation) and only after that
 \texttt{pthread\_cond\_wait} will return.
-\item When signalling that something has changed, it does not mean that after
-the change the condition will be true. Moreover,
+\item When a thread receives a signal that something has changed, it does not
+mean that after the wake up the condition will be true. Moreover,
 \texttt{pthread\_cond\_wait} can return even if no thread called
 \texttt{pthread\_cond\_signal} or \texttt{pthread\_cond\_broadcast}.
 This is another reason for testing the condition after wake-up and possibly