AppVeyor failed with a message in funny grammar saying Error uploading artifact the storage: Unable to connect to the remote server. Doesn't seem to be related to this PR.

Pinging @GaelVaroquaux, @jnothman, just in case you didn't get notified. You may want to trigger a restart of AppVeyor, or ignore it and merge.

/edit: Oh, github didn't notify me of your review -.-

@jnothman: Added the Notes header, but it seems only maintainers can access the circle artifacts to check the documentation. Hope it looks better now. (Sorry, I didn't try to install the dependencies to build the docs locally.)

Just swap the circle build number into my url above

That's the first thing I tried, but I took the deploy build... as it didn't work, I inferred I'd probably have to replace the second number in the URL as well.

I don't know why circle makes it seem otherwise

When I open any of the three circle logs, they miss the "Artifact" tab mentioned at https://circleci.com/docs/2.0/artifacts/. So I inferred I'm lacking the rights as a non-owner.

The "Notes" header increases visibility: https://19462-843222-gh.circle-artifacts.com/0/doc/modules/generated/sklearn.metrics.average_precision_score.html
Thanks for the hint! I'd say it's fine this way.

As described at http://scikit-learn.org/dev/developers/contributing.html#generated-documentation-on-circleci, you need to look at Python3. Not sure why Circle hides it, but apparently you can add #artifacts without any privilege. Alternatively, install the user script. Please go endorse my feature request at Circle CI.

As described at http://scikit-learn.org/dev/developers/contributing.html#generated-documentation-on-circleci, you need to look at Python3. Not sure why Circle hides it, but apparently you can add #artifacts without any privilege.

Oh, my bad. I read through CONTRIBUTING.md on github. Its "Documentation" section only told me about sphinx, and make would have required installing sphinx_gallery and possibly more that wasn't mentioned (it said it only needed sphinx, matplotlib and pillow), so I didn't continue.
I wasn't aware that there was a second set of more up-to-date contribution guidelines. It's mentioned at the bottom of CONTRIBUTING.md for information on conforming to the API specs and profiling code, both of which didn't apply here.
Note that this is not to blame you, just to detail how I missed all the good stuff as a sort-of-new contributor! I'll try to send a PR for CONTRIBUTING.md, unless you want to fully replace it with a link to the web page.

For the record the first sentence of CONTRIBUTING.md points to the html doc:

Note: This document is a 'getting started' summary for contributing code,
documentation, testing, and filing issues. Visit the Contributing
page
for the full contributor's guide. Please read it carefully to help make
the code review process go as smoothly as possible and maximize the
likelihood of your contribution being merged.

Having said that, I agree that things could be reorganized to make it easier for new contributors to get started. IMO CONTRIBUTING.md should be a lot shorter and add links to the dev html doc (for example the stable doc still mentions nose ...) for more details.

For the record the first sentence of CONTRIBUTING.md points to the html doc

Fair enough, but apparently that didn't help. And it's not because I didn't read that sentence -- the multi-page document I was looking at seemed to cover everything I needed extensively enough. (Does "Please read it carefully" refer to the "'getting started' summary" or the web page?)

IMO CONTRIBUTING.md should be a lot shorter and add links

That would probably work. If I had gotten the impression that this file was missing information and/or less well-maintained, I would have skipped to the web page. Linking directly to relevant sections of the long guide would lower the hurdle.
I can just offer to do this for the Documentation section, that's what I've been looking at.