README: clarify french/english usage policy
README: clarify french/english usage policy

This clarification comes from the discussion in pull-request #33:
  https://bitbucket.org/MicroJoe/progdupeupl/pull-request/33/add-indent-in-editor-when-tab-is-pressed/diff#comment-780385

progdupeupl/pdp_website,progdupeupl/pdp_website,progdupeupl/pdp_website,progdupeupl/pdp_website,progdupeupl/pdp_website