Auto-sync vendor assets & Hugo module versions + copyedits to README and CONTRIBUTING

[chalin]

• Followup to Offer Docsy as a single Hugo Module #1217
• Fixes Ensure that versions of dependencies remain in sync #1182
• Fixes Automate the updating of vendor assets #1723
• Creates a single assets/_vendor folder to hold all missing vendor assets (which for now only contains the bootstrap vendor file)
• Adds a script to sync the BS vendor file(s) from the BS NPM package, triggered by a post-install event
• Adds a script to sync Hugo modules based on the corresponding NPM package versions. Hence the NPM version are canonical
• Updates CONTRIBUTING.md:
  • Simplifies the steps in Publishing a release since some changes are not handled automatically. Also removed references to the dependencies module that was dropped via Offer Docsy as a single Hugo Module #1217
  • Other tweaks
• Explicit mention of code-of-conduct in README and CONTRIBUTING.md
• Closes Auto-sync vendor assets & Hugo module versions + copyedits to README and CONTRIBUTING #1724 by superseding it (I needed to commit to the docsy repo so that I could test from the PR branch)

[chalin]

@deining - I've tested this using docsy-example, fetching the commit from the branch of this PR, and it works AFAICT.

[deining]

Spotted a typo which needs to be corrected.
LGTM otherwise, haven't tested it, though.

[chalin]

Oh dang, tripped on the buttons somehow (or was it GH Desktop?).
Or maybe because I had two branches with the same name in my fork and here ... .
Anyhow, I didn't mean to merge this yet. I'll fix the typo in a followup commit.

[chalin]

Yeah, it wasn't the GH interface that did the merge, because it didn't squash the commits, which I have enabled by default. It must have been the GH desktop. :-(

[chalin]

My typo fix even made it into main!

[chalin]

Ok, I've reverted the commit and will resubmit a PR ... . See:

• Auto-sync vendor assets & Hugo module versions + copyedits to README and CONTRIBUTING #1733