Be louder about experimental status of windows build

[danhhz]

This "Install CockroachDB on Windows" page has a warning box but the
bolded text is "Native CockroachDB on Windows requires Windows 8 or
higher" and the experimental status is a bit hidden in the rest of the
box. This binary is almost entirely untested, so I'd suggest we swap the
bolded text to be about the experimental status of the binary.
Otherwise, I worry that users may form a bad initial impression of our
performance/stability/maturity (and perhaps don't bother contacting us
as a result).

[cockroach-teamcity]

This change is 

[danhhz]

cc @bdarnell in case you have any thoughts about the phrasing of the part about testing. I tried strengthening the language here from "has not been extensively tested by Cockroach Labs" to "is largely untested by Cockroach Labs".

[cockroach-teamcity]

Online preview: http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/4f58f8c94f53e55c5cd8083dcaa18b4d02e3d0b9/

Edited pages:

• v19.1/install-cockroachdb-windows.html
• v2.1/install-cockroachdb-windows.html

[jseldess]

Thanks, @danhhz. I'm ok with this, but note that there are some other issues around windows that we have yet to resolve. For example, this issue suggest that we should remove docker and kubernetes options for windows and encourage running in a linux vm: #3184 (comment).

@rolandcrosby is helping with this, so he may have some opinions, too.

[danhhz]

Gotcha. I'm not too tied to this. Just found myself filing an issue about it and realized that it was literally less work to PR than to finish writing up the issue. Happy to merge as an interim solution if that makes sense or throw it away if it doesn't.

[rolandcrosby]

We may want to do more with the recommendations further down on the page like Jesse mentions, but in the meantime I think it's good to be more forceful about the warning.

Reviewed 2 of 2 files at r1.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @jseldess)

[jseldess]

I'll merge for you, @danhhz. Thank you!