fix up the readme and sample .env to smooth out first dev experience (#976)

* chore: fix up the readme and sample .env to smooth out first dev experience

* fix indentation

.env.sample

@@ -3,18 +3,20 @@
 # keys (for auth) and the SECRET_KEY.
 #
 # Please use `openssl rand -hex 32` to create SECRET_KEY
-
-DATABASE_URL=postgres://user:pass@localhost:5432/outline
-DATABASE_URL_TEST=postgres://user:pass@localhost:5432/outline-test
 SECRET_KEY=generate_a_new_key
-PORT=3000
-REDIS_URL=redis://localhost:6379
+
+DATABASE_URL=postgres://user:pass@postgres:5432/outline
+DATABASE_URL_TEST=postgres://user:pass@postgres:5432/outline-test
+REDIS_URL=redis://redis:6379
+
 URL=http://localhost:3000
+PORT=3000
+
 DEPLOYMENT=self
 ENABLE_UPDATES=true
 SUBDOMAINS_ENABLED=false
 WEBSOCKETS_ENABLED=true
-DEBUG=sql,cache,presenters,events
+DEBUG=cache,presenters,events
 
 # Third party signin credentials (at least one is required)
 SLACK_KEY=get_a_key_from_slack