chore: Add missing documentation on big segment store method

Author: keelerm84

src/LaunchDarkly/Integrations/Redis.php

@@ -40,6 +40,18 @@ public static function featureRequester(ClientInterface $client, array $options
     }
 
     /**
+     * Configures a big segment store instance backed by Redis.
+     *
+     * After calling this method, store its return value in the `store` property of your Big Segment configuration:
+     *
+     *     $store = LaunchDarkly\Integrations\Redis::bigSegmentStore(["prefix" => "env1"]);
+     *     $bigSegmentsConfig = new LaunchDarkly\BigSegmentConfig(store: $store);
+     *     $config = ["big_segment" => $bigSegmentsConfig];
+     *     $client = new LDClient("sdk_key", $config);
+     *
+     * For more about using LaunchDarkly with databases, see the
+     * [SDK reference guide](https://docs.launchdarkly.com/sdk/features/storing-data).
+     *
      * @param array<string,mixed> $options
      *   - `prefix`: a string to be prepended to all database keys; corresponds
      *   to the prefix setting in ld-relay