Updates to docs for website build

[bjascob]

Minor updates to documentation for building the website locally. This closes #3648.

Description

CONTRIBUTING.md contained instructions for the old harp web server. This was replaced with a reference to website/README.md. In that file the only change was to add a note that Node 10.15 or later is required.

Note: It was suggested by @ines to also add the node version (via the "engines" param) to the package.json file. While this seemed simple enough, unfortunately I was not able to get it to produce a warning message during npm install and so did not include the change in this PR.

Types of change

Simple doc change only

Checklist

• I have submitted the spaCy Contributor Agreement.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[bjascob]

Just FYI that the npm documentation for the "engines" param says "this field is advisory only and will only produce warnings when your package is installed as a dependency.". Looks like since spacy-io is the top-level app and not a dependency, it's not going to produce a warning.

[ines]

@bjascob Thanks! And okay, I should have just read the npm docs 😅

[ines]

Looks like you might have accidentally pushed this onto the same branch as your other PR in #3646? So this PR now includes both changes. Aside from that, the changes look good!

[bjascob]

Sorry about that. I do have two separate branches but I must have pushed changes to both accidentally.

In order to fix this, from this branch I removed the test_issue3484.py and did a "git revert" on spacy/lemmatizer.py. Those files are not related to this PR. Not sure what will happen when you try to merge in these changes and the changes from PR #3646. I'm guessing you'll have a conflict and will need to choose to keep those 2 files from #3646. If that's an issue, let me know. We can just kill this entire PR/branch and I can resubmit from a clean master.