MNT: Enable circleci-artifacts-redirector

[effigies]

Changes proposed in this pull request

I've enabled Eric Larson's circleci-artifacts-redirector to make it easier to immediately open the rendered docs. This change tells it where to find the artifacts.

[auto-comment]

Thank your for raising your pull request.

Some of the fMRIPRep maintainers will review your changes as soon as time permits.
I'm attaching below a Review Checklist for the reviewers, to copy and paste
it in their review comment.

## PR Review

*Please check off boxes as applicable, and elaborate in comments below.  Your review is not limited to these topics, as described in the reviewer guide*

- [ ] As the reviewer I confirm that there are no conflicts of interest for me to review this work.

Please check what applies in the following aspects of the PR:

#### Code documentation

- [ ] New functions and modules are documented following the guidelines.
- [ ] Existing code required amendments in documentation and has been updated.
- [ ] Sufficient inline comments ensure readability by other contributors in the long term.

#### Documentation site

- [ ] The modifications to *fMRIPrep* in this PR **do not require extra documentation**. This is a common situation when a bug fix that does not change the code base substantially is submitted.
- [ ] This PR requires documentation. The corresponding documentation will be submitted as an additional PR in the future.
- [ ] This PR requires extra documentation, and will be included within this PR. Please check the boxes that apply best:
  - [ ] An existing feature is substantially modified, changing the interface and/or logic of a module.
  - [ ] A new feature is being added, therefore full documentation of it will be included
  - [ ] This PR addresses an error in existing documentation.
- [ ] Yes, all expected sections of documentation were generated by the CI build, and look as expected

#### Tests

- [ ] The new functionalities in this PR are covered by the existing tests
- [ ] New test batteries have been included with this PR

#### Data

- [ ] This PR does not require any additional data to be uploaded to OSF.
- [ ] This PR requires additional data for tests.

#### Dependencies: smriprep

- [ ] This PR does not require any update on `smriprep`; or
- [ ] `smriprep` has correctly been pinned.

#### Dependencies: niworkflows

- [ ] This PR does not require any update on `niworkflows`; or
- [ ] `niworkflows` has correctly been pinned.

#### Dependencies: sdcflows

- [ ] This PR does not require any update on `sdcflows`; or
- [ ] `sdcflows` has correctly been pinned.

#### Dependencies: Nipype

- [ ] This PR does not require any update on `nipype`; or
- [ ] `nipype` has correctly been pinned.

#### Dependencies: other

- [ ] This PR does not require any update on other dependencies; or
- [ ] other dependencies have correctly been pinned.

#### Reports generated within CI tests

- [ ] Yes, I have checked the reports of ds005 and they are not modified or the changes are as expected
- [ ] Yes, I have checked the reports of ds054 and they are not modified or the changes are as expected
- [ ] Yes, I have checked the reports of ds010 and they are not modified or the changes are as expected

### Review Comments (other than those left inline with the code)

[effigies]

Looks like it works:

Links to https://10252-53175327-gh.circle-artifacts.com//0/tmp/src/fmriprep/docs/_build/html/index.html