Improve README.

README.md

@@ -11,18 +11,23 @@ Load policy from Hibernate or save policy to it.
 
 ## Usage
 First, Introduce it in the pom.xml:
-
-    <dependency>
-        <groupId>org.casbin</groupId>
-        <artifactId>hibernate-adapter</artifactId>
-        <version>1.0.0</version>
-    </dependency>
+
+```xml
+<dependency>
+    <groupId>org.casbin</groupId>
+    <artifactId>hibernate-adapter</artifactId>
+    <version>1.0.0</version>
+</dependency>
+```
+
 Then you can use it in your project like this:
 
-    Enforcer e = new Enforcer("examples/rbac_with_domains_model.conf");
-    Adapter adapter = new HibernateAdapter(DRIVER, URL, USERNAME, PASSWORD, true);
-    e.setAdapter(adapter);
-    e.loadPolicy();
+```java
+Enforcer e = new Enforcer("examples/rbac_with_domains_model.conf");
+Adapter adapter = new HibernateAdapter(DRIVER, URL, USERNAME, PASSWORD, true);
+e.setAdapter(adapter);
+e.loadPolicy();
+```
 
 If you use Oracle, the last entry of the parameter must be set to `true`.