Improve documentation of Thread and Worker

src/thread/Worker.php

@@ -26,7 +26,14 @@ namespace pocketmine\thread;
 use const PTHREADS_INHERIT_NONE;
 
 /**
- * This class must be extended by all custom threading classes
+ * Specialized Worker class for PocketMine-MP-related use cases. It handles setting up autoloading and error handling.
+ *
+ * Workers are a special type of thread which execute tasks passed to them during their lifetime. Since creating a new
+ * thread has a high resource cost, workers can be kept around and reused for lots of short-lived tasks.
+ *
+ * As a plugin developer, you'll rarely (if ever) actually need to use this class directly.
+ * If you want to run tasks on other CPU cores, check out AsyncTask first.
+ * @see AsyncTask
  */
 abstract class Worker extends \Worker{
 	use CommonThreadPartsTrait;