add english readme

Author: wesleytong

README_EN.md

@@ -0,0 +1,33 @@
+## Note
+This project is the java implementation of tls-sig-api-v2. Previous asymmetric keys cannot use APIs of this version. To enable them to use APIs of this version,[see here](https://github.com/tencentyun/tls-sig-api-java).
+## Integration
+### maven
+``` xml
+<dependencies>
+    <dependency>
+        <groupId>com.github.tencentyun</groupId>
+        <artifactId>tls-sig-api-v2</artifactId>
+        <version>2.0</version>
+    </dependency>
+</dependencies>
+```
+
+### gradle
+```
+dependencies {
+    compile 'com.github.tencentyun:tls-sig-api-v2:2.0'
+}
+```
+
+### source code
+``` shell
+./gradlew -b user_build.gradle build
+```
+The generated jar can be found under `build/libs`. You can download it by yourself by relying on org.json.
+## use
+``` java
+import com.tencentyun.TLSSigAPIv2;
+
+TLSSigAPIv2 api = new TLSSigAPIv2(1400000000, "5bd2850fff3ecb11d7c805251c51ee463a25727bddc2385f3fa8bfee1bb93b5e");
+System.out.print(api.genSig("xiaojun", 180*86400));
+```