docs: update statess docs

[goofiw]

I updated the stateless docs to what I think it might hav meant to be, otherwise I'm not quite sure why headers would be deconstructed as it is not used.

I skipped the checklist as there it is just a doc change.

TODO:

• Make sure all of new logic is covered by tests and passes linting
• Update CHANGELOG.md with your change

[apollo-cla]

@goofiw: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[codecov-io]

Codecov Report

Merging #899 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #899   +/-   ##
=======================================
  Coverage   95.21%   95.21%           
=======================================
  Files          22       22           
  Lines        1024     1024           
  Branches      109      109           
=======================================
  Hits          975      975           
  Misses         44       44           
  Partials        5        5

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[hwillson]

Great catch - thanks @goofiw!