[texdoc] Default documentation for `yathesis`

[Denis Bitouzé]

Hi,

here is the output of `texdoc -l yathesis`

  ┌────
  │  1 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/english/README-TRANSLATION.md
  │  2 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/french/documentation/yathesis-fr.pdf
  │  3 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/french/exemples/specimen/a-plat/comue.pdf
  │  4 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/french/exemples/specimen/a-plat/labo.pdf
  │  5 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/french/exemples/specimen/a-plat/paris13.pdf
  │  6 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/french/exemples/specimen/a-plat/these.pdf
  │  7 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/french/exemples/specimen/a-plat/tiger.pdf
  │  8 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/french/exemples/specimen/a-plat/ulco.pdf
  │  9 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/README.md
  │ 10 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/french/documentation/latexmkrc
  │ 11 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/french/exemples/specimen/a-plat/latexmkrc
  └────

which doesn't make sense since `texdoc yathesis` opens
`README-TRANSLATION.md` which contains only:

  ┌────
  │ # Contributions welcome!
  │ 
  │ Currently, the `yathesis` documentation is not translated in English. In case
  │ you're interested, please contact the maintainer:
  │ `denis.bitouze at lmpa.univ-littoral.fr`
  └────

Would be much better to have (just):

  ┌────
  │  1 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/french/documentation/yathesis-fr.pdf
  │  2 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/README.md
  │  3 /usr/local/texlive/2019/texmf-dist/doc/latex/yathesis/english/README-TRANSLATION.md
  └────

If possible, many thanks in advance!

All the best.
-- 
Denis