add async library documentation

Author: FalsePattern

README.MD

@@ -15,6 +15,7 @@ The contents of the [util](src/main/java/com/falsepattern/lib/util) package so f
 | Class                                                                     | Purpose                                                                                                       |
 |---------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------|
 | [ResourceUtil](src/main/java/com/falsepattern/lib/util/ResourceUtil.java) | Provides methods for efficiently retrieving resources from SPECIFIC jar files instead of the entire classpath |
+| [Async](src/main/java/com/falsepattern/lib/util/Async.java)               | Provides asynchronous execution utilities.                                                                    |
 
 
 Anything annotated with [@StableAPI](src/main/java/com/falsepattern/lib/StableAPI.java) is guaranteed to not change in patch versions.

src/main/java/com/falsepattern/lib/util/Async.java

@@ -7,6 +7,11 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 
+/**
+ * Asynchronous utilities. Notice: you should not abuse this for anything performance-sensitive.
+ * The asynchronous worker exists primarily to run code independently of the main thread during loading.
+ * You must make sure to solve any potential deadlocks yourself!
+ */
 @StableAPI(since = "0.8.0")
 public class Async {
     public static final ExecutorService asyncWorker = Executors.newSingleThreadExecutor((runnable) -> {