nfs: new subdir Documentation/filesystems/nfs

We're adding enough nfs documentation that it may as well have its own
subdirectory.

Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/fs/isofs/export.c b/fs/isofs/export.c
index e81a305..ed752cb 100644
--- a/fs/isofs/export.c
+++ b/fs/isofs/export.c
@@ -9,7 +9,7 @@
  *
  * The following files are helpful:
  *
- *     Documentation/filesystems/Exporting
+ *     Documentation/filesystems/nfs/Exporting
  *     fs/exportfs/expfs.c.
  */