Add note about anon params

[mark-i-m]

cc @Centril @steveklabnik rust-lang/rust#41686

[steveklabnik]

This looks good to me, but I forget how we're differentiating edition differences in the text. If someone else (Either @Havvy or @alercah ) could weigh in too, that'd be great.

[Centril]

@steveklabnik I'd like the reference to be more specification-like at some point including using BNF formalisms to define things like these; but for now, this seems good enough. :)

[Havvy]

Notes are for non-normative information. Please change it to "Edition Differences" or something similar. And bold it. And then, if you're up to it, add it to conventions.md. If not, I can add it in another PR.

[Havvy]

I sent a PR against your branch. mark-i-m#1

[mark-i-m]

Thanks @Havvy! Sorry I'm a bit sluggish. I'm in a bit of time crunch.

[Havvy]

No need to apologize. You're not moving slower than anybody else on this repo. I just felt like making the changes, so I did..

[mark-i-m]

@Havvy Perhaps this can be merged now?

[Havvy]

I generally don't like merging things where I've sent commits.

[matthewjasper]

Thank you both!