Update RefinementRegionsAPI.jl Docstring

[DanielDoehring]

See current formatting:

https://trixi-framework.github.io/HOHQMesh.jl/stable/reference/#HOHQMesh.newRefinementCenter-Tuple{String,%20String,%20Array{Float64,%20N}%20where%20N,%20Float64,%20Float64}

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (158455b) 98.85% compared to head (85218cb) 98.85%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #34   +/-   ##
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  Coverage   98.85%   98.85%           
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  Files          20       20           
  Lines        1838     1838           
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  Hits         1817     1817           
  Misses         21       21           

Flag	Coverage Δ
unittests	98.85% <ø> (ø)

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Files	Coverage Δ
src/Project/RefinementRegionsAPI.jl	100.00% <ø> (ø)

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[coveralls]

coverage: 98.857%. remained the same when pulling 85218cb on DanielDoehring:main into 158455b on trixi-framework:main.