Document how to provide list types in configmap

[nrmitchi]

What this PR does / why we need it:
This is just a basic documentation addition, as I spent more time than I'd like to admit trying to find the answer here.

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[k8s-reviewable]

This change is 

[codecov-io]

Codecov Report

Merging #2124 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2124   +/-   ##
=======================================
  Coverage   36.59%   36.59%           
=======================================
  Files          68       68           
  Lines        4837     4837           
=======================================
  Hits         1770     1770           
  Misses       2799     2799           
  Partials      268      268

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[aledbf]

/approve

[aledbf]

@nrmitchi thanks!

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, nrmitchi

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