add observable create weather example

[trebor]

add a weather page like a-taste-of-observable.

@mbostock: I feel like a fun example for observable create would be a local weather dashboard. Like the old A Taste of Observable. There are some pretty convenient weather.gov APIs, and it’s pretty easy to personalize it — you just pick a location (or a weather station). And it even has lasting value if you want to automate the build of your own personal weather page.

[mbostock]

Sorry for not being clear via Slack, but I’m already working on this. 😓

[trebor]

ah, no worries. i hadn't done any work on it.

[mbostock]

Posted my draft in #623.