Flesh out packages intro

[SeanTAllen]

[rhagenson]

@SeanTAllen correct me if I am wrong, but this is referring to writing an overview for the Packages chapter (https://tutorial.ponylang.io/packages.html)?

Or is this referring to the first section in Packages (https://tutorial.ponylang.io/packages/package-system.html)?

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Either way, I am willing to help on this issue. If enough time has passed that corral has progressed we can discuss if/how package management should be included in the Packages intro.

[SeanTAllen]

The first one.

[rhagenson]

This issue involved writing a synopsis of what is to be expected from the chapter. I see the Types intro as a good example -- provides a hook for why read it, an "In this chapter, ..." 1-2 sentence summary, and a closing goals list of what a reader should know by the end of the chapter.