Links to V4 lesson

[rgaiacs]

@katrinleinweber wrote

Dear @gdevenyi, what's the status of this v4 site? https://github.com/swcarpentry/v4 seems abandoned. Over in swcarpentry/r-novice-inflammation#337 we are discussion referring to it anyway. Do you consider that advisable? Thanks for any hints here :-)

here. I think the comment didn't get enough visibility so I'm creating a issue for it.

[gdevenyi]

v4 is "archived" but its the only place with regex still present.