fix: add the snippets directory by default

[jdrouet]

This should fix https://github.com/rustwasm/wasm-pack/issues/1206

I don't know what is the way to detect if the snippets directory should be included so, by default, I include it considering it's already in the sideEffect section. Another possibility would be to add to the Cargo.toml metadata a package-json section that allows to add some files and enforce it there.

Tell me if it's ok with you or if you need some updates 😉

Make sure these boxes are checked! 📦✅

• [x] You have the latest version of rustfmt installed

$ rustup component add rustfmt

• [x] You ran cargo fmt on the code base before submitting
• [x] You reference which issue is being closed in the PR text

✨✨ 😄 Thanks so much for contributing to wasm-pack! 😄 ✨✨

[LuisOsta]

@jdrouet When do you think this PR would be merged? Do you have any idea of who we should reach out to about this?

[LuisOsta]

@drager @ashleygwilliams Is there something this PR needs before its ready to merge?

[jdrouet]

Honestly, an approval from the maintainer 😁

[LuisOsta]

I tested this on my repo and verified that it worked for us FWIW