added license mention into the README noting AGPL v3+, zadam#1708

Author: zadam

README.md

@@ -55,3 +55,7 @@ npm run start-server
 * [FancyTree](https://github.com/mar10/fancytree) - very feature rich tree library without real competition. Trilium Notes would not be the same without it.
 * [CodeMirror](https://github.com/codemirror/CodeMirror) - code editor with support for huge amount of languages
 * [jsPlumb](https://github.com/jsplumb/jsplumb) - visual connectivity library without competition. Used in [relation maps](https://github.com/zadam/trilium/wiki/Relation-map) and [link maps](https://github.com/zadam/trilium/wiki/Link-map)
+
+## License
+
+This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.