Doc: indicate the QSharedMemory::size() that the size may be bigger

Task-number: QTBUG-62468
Change-Id: I6e9274c1e7444ad48c81fffd14da78718828c4a6
Reviewed-by: Martin Smith <martin.smith@qt.io>

src/corelib/kernel/qsharedmemory.cpp

@@ -362,6 +362,9 @@ bool QSharedMemory::create(int size, AccessMode mode)
   Returns the size of the attached shared memory segment. If no shared
   memory segment is attached, 0 is returned.
 
+  \note The size of the segment may be larger than the requested size that was
+  passed to create().
+
   \sa create(), attach()
  */
 int QSharedMemory::size() const