Latest "What's New"s need PR links

[trexfeathers]

📚 Documentation

Following #3816 (comment), as many entries as possible in docs/iris/src/whatsnew/latest.rst should have links added to the associated Iris PR(s). It might also be wise to make the documentation note about adding such links a bit more insistent than the current "optionally you may also include..."

[bjlittle]

@trexfeathers Would it be possible to also include the following under this task:

• Add the associated GitHub author that contributed to delivering the content of the whatsnew, if possible
• Update the documentation to state that, apart from referencing the relevant issues/pull-request of a whatsnew entry, the GitHub author is also referenced and cited.

[trexfeathers]

Add the associated GitHub author that contributed to delivering the content of the whatsnew

@bjlittle 👍👍👍 great idea! This was actually discussed at SciPy 2020 as an important thing to do for healthy open source communities, and I notice it's already happening in Cartopy's "What's New".

[bjlittle]

@trexfeathers Cool!

Also, with regards to referencing the associated PR... as a standard to follow do you think it's best to have something like:

* whatsnew contribution. See :pull:`3818`.

Or, akin to cartopy:

* whatsnew contribution. (:pull:`3818`)

I kinda like the latter 🤔

[trexfeathers]

I agree on the latter, which leaves us free to use See :pull: and other syntaxes for more specific extra detail ("for extra info go check this out")

[bjlittle]

I agree on the latter, which leaves us free to use See :pull: and other syntaxes for more specific extra detail ("for extra info go check this out")

@trexfeathers Awesome. Let's go with that then 🚀

I'm currently making some whatsnew entries in my cube-arithmetic-post feature branch, so I'll adopt that style also to save any follow-up re-work.

And I'm assuming that you're going with the same approach as cartopy for citing authors e.g.,

John Smith contributed blah. (:pull:`xxxx`)

[trexfeathers]

Closed by #3838