docs: filesystems: convert spufs/spufs.txt to ReST

This file is at groff output format. Manually convert it to
ReST format, trying to preserve a similar output after parsed.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/9ca05fad12390931bc7da0fa2502d1a450a4b87f.1588021877.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/filesystems/spufs/index.rst b/Documentation/filesystems/spufs/index.rst
index 39553c6..939cf59 100644
--- a/Documentation/filesystems/spufs/index.rst
+++ b/Documentation/filesystems/spufs/index.rst
@@ -8,4 +8,5 @@
 .. toctree::
    :maxdepth: 1
 
+   spufs
    spu_create