Fix Wiki Page for StatusNotifierItem Markup Specification

[Nathan Schulte]

Good afternoon,

Re: https://www.freedesktop.org/wiki/Specifications/StatusNotifierItem/Markup/
...

The above page for allowable markup in StatusNotifierItem
specification is broken; there is a missing <pre> and <code> wrapping
the Image markup example (<img src="" alt="">...</img>) and so the
page renders the image HTML rather than showing the example markup.

--

Semi-related: I am unable to find specifications for the
com.canonical.dbusmenu interface referenced by the StatusNotifierItem
specification.  Is this available somewhere?  I'm looking for
specifications related to
LayoutUpdated, ItemsPropertiesUpdated signals and methods such as
GetLayout.

Also, this issue on GitLab from a few months ago discusses that the SNI spec
is a "draft" specification
(https://gitlab.freedesktop.org/xdg/xdg-specs/-/issues/44), but almost
all of the applications and systems I use leverage this specification.
Perhaps this should be moved to xdg-specs project in GitLab?

Regards,
--
Nate