Add license to README

README.md

@@ -37,3 +37,9 @@ Then install the parser for the Puppet language using the following command. Thi
 This command can also be used to update the parser to the latest version from time to time.
 
 See the Tree-sitter starter guide: https://git.savannah.gnu.org/cgit/emacs.git/tree/admin/notes/tree-sitter/starter-guide?h=emacs-29
+
+## License
+
+Puppet Treesitter Mode is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
+
+Puppet Treesitter Mode is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.