docs: document retry settings in sample (#1214)

* docs: document retry settings in sample

* fix: change timeout values back to match doc

Author: olavloite

samples/snippets/src/main/java/com/example/spanner/CustomTimeoutAndRetrySettingsExample.java

@@ -53,14 +53,23 @@ static void executeSqlWithCustomTimeoutAndRetrySettings(
         .setRetrySettings(
             RetrySettings.newBuilder()
                 // Configure retry delay settings.
+                // The initial amount of time to wait before retrying the request.
                 .setInitialRetryDelay(Duration.ofMillis(500))
+                // The maximum amount of time to wait before retrying. I.e. after this value is
+                // reached, the wait time will not increase further by the multiplier.
                 .setMaxRetryDelay(Duration.ofSeconds(64))
+                // The previous wait time is multiplied by this multiplier to come up with the next
+                // wait time, until the max is reached.
                 .setRetryDelayMultiplier(1.5)
 
                 // Configure RPC and total timeout settings.
+                // Timeout for the first RPC call. Subsequent retries will be based off this value.
                 .setInitialRpcTimeout(Duration.ofSeconds(60))
+                // The max for the per RPC timeout.
                 .setMaxRpcTimeout(Duration.ofSeconds(60))
+                // Controls the change of timeout for each retry.
                 .setRpcTimeoutMultiplier(1.0)
+                // The timeout for all calls (first call + all retries).
                 .setTotalTimeout(Duration.ofSeconds(60))
                 .build());
     // Create a Spanner client using the custom retry and timeout settings.