docs: filesystems: convert spufs/spu_create.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 <[email protected]>
Link: https://lore.kernel.org/r/4d42e97d5560a79bd5dd443c592be04f9ae9a757.1588021877.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <[email protected]>
diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst
index c658ddee..5fb2b21 100644
--- a/Documentation/filesystems/index.rst
+++ b/Documentation/filesystems/index.rst
@@ -105,6 +105,7 @@
    ramfs-rootfs-initramfs
    relay
    romfs
+   spufs/index
    squashfs
    sysfs
    sysv-fs