Update README with context caveats

[Chnapy]

Hi,

I wasted lot of debugging time because of context issues, similar to #93. Thanks to this issue and its comments I resolved my issues, but I think that talk about it in README would be a big help since it's a strange behavior + not a react-pixi-fiber bug (+ for people like me that waited long time before digging "context" related issues 🙈 ).

So I did it to the "caveats" section. If you're ok with keeping it, feel free to suggest changes or even make changes directly 👍

(btw thanks for this lib, you saved me lot of work, saving me from duplicating React logic in Pixi environment ❤️ )

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[michalochman]

Thanks @Chnapy, great idea, thanks for contributing! I will merge as is as the text is understandable.

[0xdevalias]

This solution is also pointed out here: michalochman/react-pixi-fiber#93.

I'll close this issue now as it is not related to this lib but to React Context API.

In case anyone else stumbles here from Google/etc, react-pixi-fibre now lists this in it's 'caveats' section of the README:

• https://github.com/michalochman/react-pixi-fiber#react-context-api-limitations

This links to the following React issue:

• Imperative wrappers can't access current context value in commit phase facebook/react#13336

Which seems to have been closed by this PR:

• Support class component static contextType attribute facebook/react#13728

Which seems to have been included in the React 16.6.0 changelog in this PR:

• Add 16.6.0 changelog facebook/react#13927

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I haven't looked any deeper into things that that yet, but at least in theory, I would expect that the React side of this bug/issue/weirdness should be fixed now. So it may 'just work'.

Originally posted by @0xdevalias in pixijs/pixi-react#77 (comment)