chore: created .env.example file to store env variables

packages/hoppscotch-backend/.env.example

@@ -0,0 +1,15 @@
+# Prisma Config
+DATABASE_URL=postgresql://postgres:testpass@dev-db:5432/hoppscotch
+
+# Postmark Config
+POSTMARK_SERVER_TOKEN=postmark-token-here
+POSTMARK_SENDER_EMAIL=support@hoppscotch.io
+
+# Auth Tokens Config
+JWT_SECRET='add some secret here'
+REFRESH_TOKEN_VALIDITY="168h" # Default validity is 7 days
+ACCESS_TOKEN_VALIDITY="30s" # Default validity is 1 day
+
+# Hoppscotch App Domain Config
+APP_DOMAIN="http://localhost:3000"
+