add CSRF_TRUSTED_ORIGINS to settings

.env.example

@@ -4,6 +4,9 @@ DEBUG=true
 # This is not the real key used in prod
 SECRET_KEY=(4sjxvhz@m5$0a$j0_pqicnc$s!vbve)z+&++m%g%bjhlz4+g2
 
+# comma-separated values
+CSRF_TRUSTED_ORIGINS=
+
 DATABASE_URL=sqlite:///db.sqlite3
 # uncomment the next line if you want to use a postgres database
 #DATABASE_URL=postgres://user:password@127.0.0.1:5432/sith