updated .gitignore

.gitignore

 # Operating system files
 .DS_Store
 Thumbs.db
+#backend
+src/backend/__pycache__/
+src/backend/api/
+src/backend/backend_utilities/
+src/backend/cache/
+src/backend/endpoints/
+src/backend/middleware/
+src/backend/core/
 
+#frontend
 # node_modules becomes very big after npm install
 src/frontend/node_modules