[m-rev.] for post-commit review: add a link to the Mercury Crash Course

[Julien Fischer]

On Sun, 31 May 2020, Zoltan Somogyi wrote:

> For review and installation by Julien.

That's fine; I'll update the website once you push the changes.

> You may want to install my recent changes to the user guide as well,
> with or without review :-)

They're already installed.  I've reviewed them, I just haven't caught up
with my mail this weekend.

Julien.