add some doc (#1100)

docs/cn/Application-toolkit-trace-CN.md

@@ -17,3 +17,7 @@ modelAndView.addObject("traceId", TraceContext.traceId());
 _示例代码，仅供参考_
 
 * 对任何需要追踪的方法，使用 `@Trace` 标注，则此方法会被加入到追踪链中。
+* 在被追踪的方法中自定义 tag.
+```java
+ActiveSpan.tag("my_tag", "my_value");
+```

docs/en/Application-toolkit-logback-1.x.md

@@ -1,10 +1,10 @@
 * Dependency the toolkit, such as using maven or gradle
 ```xml
-   <dependency>
-      <groupId>org.apache.skywalking</groupId>
-      <artifactId>skywalking-toolkit-logback-1.x</artifactId>
-      <version>{project.release.version}</version>
-   </dependency>
+    <dependency>
+         <groupId>org.apache.skywalking</groupId>
+         <artifactId>apm-toolkit-logback-1.x</artifactId>
+         <version>{project.release.version}</version>
+     </dependency>
 ```
 
 * set `%tid` in `Pattern` section of logback.xml

docs/en/Application-toolkit-trace.md

@@ -17,3 +17,7 @@ modelAndView.addObject("traceId", TraceContext.traceId());
 _Sample codes only_
 
 * Add `@Trace` to any method you want to trace. After that, you can see the span in the Stack.
+* Add custom tag in  the context of traced method .
+```java
+ActiveSpan.tag("my_tag", "my_value");
+```