message: Add license for latex grammar
diff: # Grammars and language configurations
  +## LaTeX
  +
  +The LaTeX grammar `LaTeX.tmLanguage.json` is based on https://github.com/textmate/latex.tmbundle/blob/master/Syntaxes/LaTeX.plist but has been largely modified. The original file falls under the following license
  +
  + Permission to copy, use, modify, sell and distribute this
  + software is granted. This software is provided "as is" without
  + express or implied warranty, and with no claim as to its
  + suitability for any purpose.
  +
  ## Combined LaTeX/Markdown
  The file `markdown-latex-combined.tmLanguage.json` is generated from the Markdown grammar included in VSCode and is licensed as described in `markdown-latex-combined-license.txt`.
  