Release notes for hooks and observers

[alice-i-cecile]

Fixes #1409. Hooks apparently didn't get an issue, but that's fine.

I've decided to tackle these together, focusing on the context of "why and how should I use all these different tools".

Talking to users about the feature, this was the primary confusion / area to clarify: not the API.

[torsteingrindvik]

Personally I'd love to read this section and immediately know how to employ hooks and/or observers to a common problem that is an awkward fit without them, but I didn't find one right away.

There seems to be a hint towards this

data (like indexes or hierarchies) exists, even momentarily, in an invalid state

Could a sentence or two about a concrete example of an invalid state (and why it's safer or totally fixed by observers/hooks) be added somewhere? I think that would help me at least

[iiYese]

Some suggestions but looks good.

[alice-i-cecile]

@torsteingrindvik does the new example help clarify things for you? :)

[torsteingrindvik]

@torsteingrindvik does the new example help clarify things for you? :)

Yes, thank you!

This example lead me to immediately consider a few components I have in my own apps which contain references to other entities, and now I have a mental hook to consider this new feature for those.