bug#50728: Update Pandoc (just on my machine)

[vidak]

I know that there is this issue:

http://issues.guix.gnu.org/39798

And it was closed because Guix wants to stay with the LTS version of
Haskell.

But I need to use some features that come in later versions of pandoc.

A few of my static site generator projects break because I need features
that come after 2.7.x, which is the version that Guix packages.

Can someone explain to me how to package the latest pandoc just on my
own computer?

Thanks.

~vidak