move WDL language links?

[jayoung]

in the 'submit-jobs-tab' section of the tutorial, I read the following info:
"There is emerging documentation about the WDL specification itself being generated by the openWDL community here. Also, there is some useful, though very detailed, information in the openWDL GitHub repo for the specification itself where you can learn more."

That's great! But it seems wierd to me to put it in that section - it's about how to write WDLs, not about how to submit jobs.

In fact, I have a very big picture comment - I had misunderstood what this course was going to cover. I thought I'd be learning how to write WDLs. It's totally fine that I'm not, but it would be great to set expectations, and to help me figure out where I can learn that.

Suggestion on how: at the very beginning, either in the front page or the intro it would be good to have a "What is WDL?" section. There, we set expectations that we WON'T be learning WDL here, but provide links to places we can learn WDL, and the links to the WDL specs that are currently in the 'submit jobs tab' section of the guide.