Docs: clarify action merging behavior when combining slices

[unbeauvoyage]

When I tried the code myself, I wasn't expecting the actions to be merged and thought it was a mistake. It was concluded, in another discussion that 'this "action merging" behavior is one of features of this fairly opinionated lib, so it should be clearly stated somewhere'. To prevent similar confusion when others try it too, I thought that it would be best not to let it be forgotten and that "combining slices" part in the getting started section, right after the relevant example, is a good place for a clarification. Feel free to edit the change or altogether reject it if it is not the proper place.

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Below is how it will look in the docs:

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[dai-shi]

Thanks for adding the note. Looks good to me!

Just to let you know, I understand this behavior can be confusing. If it's not welcomed by many users, this library may reconsider its opinion in the future.

[unbeauvoyage]

@dai-shi
In real world applications slices will usually be in different files and there could be dozens of properties (even hundreds, if the app is using a single store), and it might cause name collisions and bugs. There will be higher likelihood of developers being caught off guard and an additional layer they need to be aware of. Since this library already provides withActions() for store level actions, where one can easily compose individual actions anyway, I would humbly suggest that it might be worth reconsidering this approach.

[dai-shi]

Thanks for the suggestion. Can you open a new issue to discuss further?

I don't dislike the suggested approach. It's straightforward and the implementation can be simpler.