Added deprecation notice

[j-rewerts]

Outlined our current timeline for deprecation.

@clayreimann I'd love to get your eyes on this, just to make sure I'm not pushing something you or the original authors don't want.

[codecov-io]

Codecov Report

Merging #573 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #573   +/-   ##
=======================================
  Coverage   90.93%   90.93%           
=======================================
  Files          12       12           
  Lines         419      419           
=======================================
  Hits          381      381           
  Misses         38       38

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