Document that Tomcat's maxQueueCapacity need to be greater than 0

Closes gh-42726

Author: mhalbritter

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java

@@ -937,7 +937,8 @@ public static class Threads {
 			private int minSpare = 10;
 
 			/**
-			 * Maximum capacity of the thread pool's backing queue.
+			 * Maximum capacity of the thread pool's backing queue. This setting only has
+			 * an effect if the value is greater than 0.
 			 */
 			private int maxQueueCapacity = 2147483647;