docs(configuration): add redis as session storage

docs/sources/installation/configuration.md

@@ -373,7 +373,7 @@ Set to `true` to enable auto sign up of users who do not exist in Grafana DB. De
 
 
 ### provider
 ### provider
 
 
-Valid values are `memory`, `file`, `mysql`, `postgres`, `memcache`. Default is `file`.
+Valid values are `memory`, `file`, `mysql`, `postgres`, `memcache` or `redis`. Default is `file`.
 
 
 ### provider_config
 ### provider_config
 
 
@@ -384,6 +384,7 @@ session provider you have configured.
 - **mysql:** go-sql-driver/mysql dsn config string, e.g. `user:password@tcp(127.0.0.1:3306)/database_name`
 - **mysql:** go-sql-driver/mysql dsn config string, e.g. `user:password@tcp(127.0.0.1:3306)/database_name`
 - **postgres:** ex:  user=a password=b host=localhost port=5432 dbname=c sslmode=disable
 - **postgres:** ex:  user=a password=b host=localhost port=5432 dbname=c sslmode=disable
 - **memcache:** ex:  127.0.0.1:11211
 - **memcache:** ex:  127.0.0.1:11211
+- **redis:** ex: `addr=127.0.0.1:6379,pool_size=100,db=grafana`
 
 
 If you use MySQL or Postgres as the session store you need to create the
 If you use MySQL or Postgres as the session store you need to create the
 session table manually.
 session table manually.