Fix directory structure in the best practices guide on parametrizations.

[tobiasraabe]

Closes #205

[codecov]

Codecov Report

Merging #208 (115893c) into main (42da034) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #208   +/-   ##
=======================================
  Coverage   92.78%   92.78%           
=======================================
  Files          75       75           
  Lines        6872     6872           
=======================================
  Hits         6376     6376           
  Misses        496      496           

Flag	Coverage Δ
end_to_end	78.62% <ø> (ø)
integration	41.93% <ø> (ø)
unit	70.03% <ø> (ø)

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