Precise documentation of file-notify-add-watch

* doc/lispref/os.texi (File Notifications):
* lisp/filenotify.el (file-notify-add-watch): Precise, that
watching a directory includes reports on file changes for some
backends.  (Bug#51146)

doc/lispref/os.texi

@@ -3124,8 +3124,9 @@ watch for file attribute changes, like permissions or modification
 time
 @end table
 
-If @var{file} is a directory, changes for all files in that directory
-will be notified.  This does not work recursively.
+If @var{file} is a directory, @code{change} watches for file creation
+or deletion in that directory.  Some of the file notification backends
+report also file changes.  This does not work recursively.
 
 When any event happens, Emacs will call the @var{callback} function
 passing it a single argument @var{event}, which is of the form

lisp/filenotify.el

@@ -390,7 +390,9 @@ include the following symbols:
                         permissions or modification time
 
 If FILE is a directory, `change' watches for file creation or
-deletion in that directory.  This does not work recursively.
+deletion in that directory.  Some of the file notification
+backends report also file changes.  This does not work
+recursively.
 
 When any event happens, Emacs will call the CALLBACK function passing
 it a single argument EVENT, which is of the form

test/lisp/filenotify-tests.el

@@ -743,7 +743,7 @@ delivered."
 	     ;; the directory.  Except for
 	     ;; GFam{File,Directory}Monitor, GPollFileMonitor and
 	     ;; kqueue.  And GFam{File,Directory}Monitor and
-	     ;; GPollFileMonitordo not raise a `changed' event.
+	     ;; GPollFileMonitor do not raise a `changed' event.
 	     ((memq (file-notify--test-monitor)
                     '(GFamFileMonitor GFamDirectoryMonitor GPollFileMonitor))
 	      '(created deleted stopped))