:construction: Updated env sample with new variables

backend/.env.sample

 # API host:port
 API_HOST=localhost
 API_PORT=3001
+APP_SECRET=somesecret
+APP_SESSION_SALT=a;sldkja;ldksfja;sldkj
 
 USE_LOCAL_DB=true
 DB_TYPE=mysql
 
-
 # Extra pepper for auth encryption
 PEPPER=kosho
 APP_SECRET=mysecret
 DB_USER=root
 DB_ROOT_PASSWORD=root
 
-
 # Config for remote planet scale production dB
 PSCALE_DB_HOST=planet-scale-db
 PSCALE_DB_PORT=3306