docs/tools/virtiofsd: Fix bad rst syntax

For literal blocks, there has to be an empty line after the two colons,
and the block itself should be indented.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20210607180015.924571-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

docs/tools/virtiofsd.rst

@@ -239,7 +239,7 @@ xattr-mapping Examples
 
 ::
 
--o xattrmap=":prefix:all::user.virtiofs.::bad:all:::"
+ -o xattrmap=":prefix:all::user.virtiofs.::bad:all:::"
 
 
 This uses two rules, using : as the field separator;
@@ -250,7 +250,8 @@ the host set.
 This is equivalent to the 'map' rule:
 
 ::
--o xattrmap=":map::user.virtiofs.:"
+
+ -o xattrmap=":map::user.virtiofs.:"
 
 2) Prefix 'trusted.' attributes, allow others through
 
@@ -277,7 +278,8 @@ through.
 This is equivalent to the 'map' rule:
 
 ::
--o xattrmap="/map/trusted./user.virtiofs./"
+
+ -o xattrmap="/map/trusted./user.virtiofs./"
 
 3) Hide 'security.' attributes, and allow everything else