Fix release instructions

[darrnshn]

This patch updates the release instructions in CONTRIBUTING.md:

• Add instructions to get fresh clone of repo.
• Added --ignore-unmatch to git rm .gitignore because .gitignore may not exist.
• Clarify where to push things.
• Replaced git push HEAD:refs/heads/master with git push origin master because the former simply did not work.
• Add more detailed instructions for drafting the release on GitHub.

Note that this diff contains an irrelevant commit Fix missing web-animations.min.js issue. This will disappear once that commit is pushed to dev by @ewilligers .

[alancutter]

Yay!

[alancutter]

Let's add a step to verify that git remote -v shows that origin points to github.com/web-animations/web-animations-js.

[alancutter]

Steps "Add versioned release notes to History.md" and "Commit the above changes" should probably also be using origin.

[darrnshn]

Hmm what happens if their git remote -v doesn't show the right value? If it's a fork, I'm guessing it'll point to their own forked repo?

[alancutter]

In that case the least invasive way to resolve it is to make a new clone of the central repo and work in that.

[darrnshn]

Cool, so maybe for releases, we use a clone, but for code changes, use fork? I'll add a step in the beginning for cloning the repo.

[alancutter]

Sure that works. If the release process doesn't assume the existence of a repository that gives it more guarantees on the repo's state.

[darrnshn]

Cool, uploaded new commits, PTAL

[alancutter]

This change is unrelated and should be kept separate.

[darrnshn]

Yep, it looks like I didn't actually push to origin dev (not sure if I was meant to).
@ewilligers will be pushing that commit to origin dev soon so this diff should disappear.

[alancutter]

Mmm, the instructions should probably say to push to origin/dev to avoid this problem in future.

[alancutter]

This change is unrelated and should be kept separate.