tools/memory-model/Documentation: Fix SRCU section in explanation.txt

The SRCU read-side critical sections describes the difference between
srcu_down_read()/srcu_up_read() and srcu_read_lock()/srcu_read_unlock()
in a way that a last pair must occur on the same CPU.

This is not true, the srcu_read_unlock() can happen on any CPU, but it
must be performed by the same task that invoked srcu_read_lock().

Signed-off-by: Uladzislau Rezki (Sony) <[e-mail]>
Signed-off-by: Paul E. McKenney <[e-mail]>

tools/memory-model/Documentation/explanation.txt

···
 
 3.	The srcu_down_read() and srcu_up_read() primitives work
 	exactly like srcu_read_lock() and srcu_read_unlock(), except
-	that matching calls don't have to execute on the same CPU.
+	that matching calls don't have to execute within the same context.
 	(The names are meant to be suggestive of operations on
 	semaphores.)  Since the matching is determined by the domain
 	pointer and index value, these primitives make it possible for