Update AutoSizer documentation

[NadiaIdris]

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PR Description

Added more info on how to fix AutoSizer height 0 issue if AutoSizer is a descendant of a flex container.

[NadiaIdris]

@reginadiana - Thanks for approving the PR. I was wondering when this might be merged (I don't have write access to this repo)?

[reginadiana]

@reginadiana - Thanks for approving the PR. I was wondering when this might be merged (I don't have write access to this repo)?

I think just the @bvaughn can approve :(