chore: update docs and suggestions

README.md

@@ -14,6 +14,7 @@ Laravel database driver for Google Cloud Spanner
 - [gRPC extension](https://cloud.google.com/php/grpc)
 - [protobuf extension](https://cloud.google.com/php/grpc#install_the_protobuf_runtime_library) (not required, but strongly recommended)
 - Currently only supports Spanner running GoogleSQL (PostgreSQL mode not supported) 
+- `sysvmsg`, `sysvsem`, `sysvshm` extensions (strongly recommended for better performance)
 
 ## Installation
 Put JSON credential file path to env variable: `GOOGLE_APPLICATION_CREDENTIALS`
@@ -328,10 +329,19 @@ This means that if you make any modifications through the above functions and th
 
 
 ### SessionPool and AuthCache
+
 In order to improve the performance of the first connection per request, we use [AuthCache](https://github.com/googleapis/google-cloud-php#caching-access-tokens) and [CacheSessionPool](https://googleapis.github.io/google-cloud-php/#/docs/google-cloud/latest/spanner/session/cachesessionpool).
 
-By default, laravel-spanner uses [Filesystem Cache Adapter](https://symfony.com/doc/current/components/cache/adapters/filesystem_adapter.html) as the caching pool. If you want to use your own caching pool, you can extend ServiceProvider and inject it into the constructor of `Colopl\Spanner\Connection`.
+By default, this library uses [Filesystem Cache Adapter](https://symfony.com/doc/current/components/cache/adapters/filesystem_adapter.html) as the caching pool. If you want to use your own caching pool, you can extend ServiceProvider and inject it into the constructor of `Colopl\Spanner\Connection`.
+
+The initialization of each session takes about a second, so warming up the sessions during the boot up phase of your
+server is recommended. This can be achieved by running the `php artisan spanner:warmup` command. You can set the number
+of sessions to warm up by setting the `connections.{name}.session_pool.maxSessions` option in `config/database.php`
 
+Similarly, the sessions remain active for 60 minutes after use so deleting the sessions during the shutdown phase 
+of your server is recommended. This can be achieved by running the `php artisan spanner:cooldown` command.
+
+```php
 
 ### Queue Worker
 

composer.json

@@ -46,6 +46,7 @@
     "test": "phpunit"
   },
   "suggest": {
+    "ext-protobuf": "Native support for protobuf is available. Will use pure PHP implementation if not present.",
     "ext-sysvmsg": "Can use SemaphoreLock for session handling. Will use FileLock if not present.",
     "ext-sysvsem": "Can use SemaphoreLock for session handling. Will use FileLock if not present.",
     "ext-sysvshm": "Can use SemaphoreLock for session handling. Will use FileLock if not present."