Edits to packaging-and-publishing tutorial step.

[data-pup]

This makes some minor changes to update the packaging-and-publishing file in the tutorial. This changes the init command to build, now that #216 has landed. Additionally, the --out-dir flag from #263 is mentioned, so this shouldn't be merged until that PR is complete.

Aside from those changes, there are some minor edits that are somewhat subjective, but improve readability (imo). Adding a period for consistency in the build command's description, removing contractions, etc.

Happy to adjust these edits if anybody has feedback, or if I made any mistakes here 😺 ❤️

---

Make sure these boxes are checked! 📦✅

• You have the latest version of rustfmt installed and have your
  cloned directory set to nightly

$ rustup override set nightly
$ rustup component add rustfmt-preview --toolchain nightly

• You ran rustfmt on the code base before submitting
• You reference which issue is being closed in the PR text

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

[fitzgen]

I'm hesitant to merge docs PRs at the moment, because Ashley had big plans for reworking them that are only half landed, and I don't want to force here to rebase a bunch. I think we should wait on merging this PR until she can get all her vision implemented.

[data-pup]

That definitely makes sense! I figured it couldn't hurt to open this, but I'm happy to handle any merge conflicts if need be in the future 😸

[ashleygwilliams]

hey- sorry this got stuck in neverland. i would absolutely accept a PR with these changes but i imagine that opening a new PR would make more sense. let me know what you think and again, sorry for the trouble.