Make docstring escape sequence proof

[maltevesper]

Matters on Windows, where the path can contain backslashes, i.e. C:\User... -> unknown unicode escape sequence.

Simply making the docstring in the template a raw string avoids the issue.

[codecov[bot]]

Codecov Report

Merging #43 (4ae2274) into main (5853f9b) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #43   +/-   ##
=======================================
  Coverage   93.39%   93.39%           
=======================================
  Files          18       18           
  Lines         560      560           
=======================================
  Hits          523      523           
  Misses         37       37           

Flag	Coverage Δ
unittests	93.39% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pytest_docker_tools/builder.py	100.00% <ø> (ø)

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[maltevesper]

@Jc2k : What do I need to do to get this (tiny, but vital) fix merged?