Fix missing license disclaimer in file headers

[roanutil]

Add the missing license disclaimer to the auto-generated file headers.

[codecov]

Codecov Report

Merging #10 (64ea4d3) into main (cb64d3b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #10   +/-   ##
=======================================
  Coverage   81.34%   81.34%           
=======================================
  Files          23       23           
  Lines        1410     1410           
=======================================
  Hits         1147     1147           
  Misses        263      263           

Files Changed	Coverage Δ
Sources/ArgumentEncoding/ArgumentGroup.swift	88.39% <ø> (ø)
Sources/ArgumentEncoding/CaseConverter.swift	90.00% <ø> (ø)
Sources/ArgumentEncoding/Command.swift	80.00% <ø> (ø)
...ources/ArgumentEncoding/CommandRepresentable.swift	100.00% <ø> (ø)
...gumentEncoding/DecoderUserInfo+OptionHelpers.swift	50.00% <ø> (ø)
...entEncoding/DecoderUserInfo+OptionSetHelpers.swift	53.33% <ø> (ø)
Sources/ArgumentEncoding/Flag.swift	100.00% <ø> (ø)
...rgumentEncoding/TopLevelCommandRepresentable.swift	100.00% <ø> (ø)
...sts/ArgumentEncodingTests/ArgumentGroupTests.swift	99.42% <ø> (ø)
...umentEncodingTests/CommandRepresentableTests.swift	97.43% <ø> (ø)
... and 13 more