Add GPL 3.0 licence

main.py

@@ -1,3 +1,18 @@
+# This file is part of Pythagoras.
+#
+# Pythagoras 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.
+#
+# Pythagoras 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.
+#
+# You should have received a copy of the GNU General Public License
+# along with Pythagoras. If not, see <https://www.gnu.org/licenses/>.
+
 from fastapi import FastAPI, File, Request, WebSocket, WebSocketDisconnect, BackgroundTasks, HTTPException
 from fastapi.responses import JSONResponse, FileResponse
 import logging