add environments' description

apollo-core/src/main/java/com/ctrip/framework/apollo/core/enums/Env.java

@@ -3,6 +3,19 @@ package com.ctrip.framework.apollo.core.enums;
 import com.google.common.base.Preconditions;
 
 /**
+ * Here is the brief description for all the predefined environments:
+ * <ul>
+ *   <li>LOCAL: Local Development environment, assume you are working at the beach with no network access</li>
+ *   <li>DEV: Development environment</li>
+ *   <li>FWS: Feature Web Service Test environment</li>
+ *   <li>FAT: Feature Acceptance Test environment</li>
+ *   <li>UAT: User Acceptance Test environment</li>
+ *   <li>LPT: Load and Performance Test environment</li>
+ *   <li>PRO: Production environment</li>
+ *   <li>TOOLS: Tooling environment, a special area in production environment which allows
+ * access to test environment, e.g. Apollo Portal should be deployed in tools environment</li>
+ * </ul>
+ *
  * @author Jason Song(song_s@ctrip.com)
  */
 public enum Env{