Chapter 1 "Understanding Fable" updates for Fable v4

[Zaid-Ajaj]

Requires PR fable-getting-started#31 to be merged first.

This PR updates the first chapter to use an updated fable-getting-started template using Fable v4 being pulled from dotnet tools and using simplified webpack setup

cc @MangelMaxime @alfonsogarciacaro it would be amazing if you could glance over the content to see if it is all good

[MangelMaxime]

I didn't run the project but I think the explanations are correct.

If I remember correctly how --runFast works, the first time that the user will run npm run watch on a clean project he will have to wait for the initial compilation even if webpack is started because not compiled files will exist yet. I think webpack will report an error message (in red).

So I don't know if you prefer to use --run so start webpack only when the first compilation of Fable is done.

I am mentioning that only in case you want to avoid a new user to have a red message printed on its first run.

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I think I would probably add the content of package.json (just the interesting sections) in the documentation directly because, when reading the page I was looking at what npm run start does. Because, npm run start by itself can do anything.

[HarryMcCarney]

+1