Document that Watcher.Remove returns nil if the Watcher is closed

This was already tested in TestClose/error_after_closed; just wasn't
documented.

backend_fen.go

@@ -270,6 +270,8 @@ func (w *Watcher) AddWith(name string, opts ...addOpt) error {
 // /tmp/dir and /tmp/dir/subdir then you will need to remove both.
 //
 // Removing a path that has not yet been added returns [ErrNonExistentWatch].
+//
+// Returns nil if [Watcher.Close] was called.
 func (w *Watcher) Remove(name string) error {
 	if w.isClosed() {
 		return nil

backend_inotify.go

@@ -285,6 +285,8 @@ func (w *Watcher) AddWith(name string, opts ...addOpt) error {
 // /tmp/dir and /tmp/dir/subdir then you will need to remove both.
 //
 // Removing a path that has not yet been added returns [ErrNonExistentWatch].
+//
+// Returns nil if [Watcher.Close] was called.
 func (w *Watcher) Remove(name string) error {
 	if w.isClosed() {
 		return nil

backend_kqueue.go

@@ -292,6 +292,8 @@ func (w *Watcher) AddWith(name string, opts ...addOpt) error {
 // /tmp/dir and /tmp/dir/subdir then you will need to remove both.
 //
 // Removing a path that has not yet been added returns [ErrNonExistentWatch].
+//
+// Returns nil if [Watcher.Close] was called.
 func (w *Watcher) Remove(name string) error {
 	return w.remove(name, true)
 }

backend_other.go

@@ -166,4 +166,6 @@ func (w *Watcher) AddWith(name string, opts ...addOpt) error { return nil }
 // /tmp/dir and /tmp/dir/subdir then you will need to remove both.
 //
 // Removing a path that has not yet been added returns [ErrNonExistentWatch].
+//
+// Returns nil if [Watcher.Close] was called.
 func (w *Watcher) Remove(name string) error { return nil }

backend_windows.go

@@ -262,6 +262,8 @@ func (w *Watcher) AddWith(name string, opts ...addOpt) error {
 // /tmp/dir and /tmp/dir/subdir then you will need to remove both.
 //
 // Removing a path that has not yet been added returns [ErrNonExistentWatch].
+//
+// Returns nil if [Watcher.Close] was called.
 func (w *Watcher) Remove(name string) error {
 	if w.isClosed() {
 		return nil

mkdoc.zsh

@@ -120,6 +120,8 @@ remove=$(<<EOF
 // /tmp/dir and /tmp/dir/subdir then you will need to remove both.
 //
 // Removing a path that has not yet been added returns [ErrNonExistentWatch].
+//
+// Returns nil if [Watcher.Close] was called.
 EOF
 )