Improve doc based on feedback

[ewjoachim]

Looks like Procrastinate was featured on the orange website. Let's browse the answers and see if there is interesting feedback to gather:

• Things we can do better
• Things we could explain better in the docs

Ping @noodlesuk: if you're the OP from HN, thanks :)

[ewjoachim]

I believe we could at least take a look at the alternative libs mentionned and add them to our list in the discussion page.

[kbakk]

Link to discussion: https://news.ycombinator.com/item?id=30126152