docs: improve usage section documentation

Author: shiqimei

README.md

@@ -2,36 +2,32 @@
 
 > Self-maintained QuickJS Android Bindings.
 
-## Download
+## Usage
 
-1. Download latest `.aar` from [release](https://github.com/shiqimei/quickjs-android/releases) page.
+1. Download the latest `.aar` archive from [release](https://github.com/shiqimei/quickjs-android/releases) page;
 2. In Android Studio: `File > New > New Module > Import .JAR/.AAR Package`, locate `.aar`, click `Finish`.
 
-## Usage
-
-### Evaluate Javascript Scripts
-
-```Java
-QuickJS quickJS = new QuickJS.Builder().build();
-try (JSRuntime runtime = quickJS.createJSRuntime()) {
-  try (JSContext context = runtime.createJSContext()) {
-    String script1 = "" +
-        "function fibonacci(n) {" +
-        "  if (n == 0 || n == 1) return n;" +
-        "  return fibonacci(n - 1) + fibonacci(n - 2);" +
-        "}";
-    // Evaluate a script without return value
-    context.evaluate(script1, "fibonacci.js");
-
-    String script2 = "fibonacci(10);";
-    // Evaluate a script with return value
-    int result = context.evaluate(script2, "fibonacci.js", int.class);
-    assertEquals(55, result);
+  ```Java
+  QuickJS quickJS = new QuickJS.Builder().build();
+  try (JSRuntime runtime = quickJS.createJSRuntime()) {
+    try (JSContext context = runtime.createJSContext()) {
+      String script1 = "" +
+          "function fibonacci(n) {" +
+          "  if (n == 0 || n == 1) return n;" +
+          "  return fibonacci(n - 1) + fibonacci(n - 2);" +
+          "}";
+      // Evaluate a script without return value
+      context.evaluate(script1, "fibonacci.js");
+
+      String script2 = "fibonacci(10);";
+      // Evaluate a script with return value
+      int result = context.evaluate(script2, "fibonacci.js", int.class);
+      assertEquals(55, result);
+    }
   }
-}
-```
+  ```
 
-See [Usages](./Usages.md) for advanced usages.
+  See [Usages.md](./Usages.md) for advanced usages.
 
 ## Develop