Update data.rst

[aribornstein]

Added data flow gif to the docs

What does this PR do?

Fixes # (issue)

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[codecov]

Codecov Report

Merging #356 (b546108) into master (55dddea) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #356   +/-   ##
=======================================
  Coverage   88.82%   88.82%           
=======================================
  Files          80       80           
  Lines        4144     4144           
=======================================
  Hits         3681     3681           
  Misses        463      463           

Flag	Coverage Δ
gpu	?
pytest	?
unittests	88.82% <ø> (ø)

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[ethanwharris]

Nice! LGTM