update tt docs. alibaba#2771

Author: hengyunabc

core/src/main/java/com/taobao/arthas/core/command/monitor200/TimeTunnelCommand.java

@@ -168,7 +168,7 @@ public void setRegEx(boolean regEx) {
     }
 
     @Option(shortName = "n", longName = "limits")
-    @Description("Threshold of execution times")
+    @Description("Threshold of execution times, default value 100")
     public void setNumberOfLimit(int numberOfLimit) {
         this.numberOfLimit = numberOfLimit;
     }

site/docs/doc/tt.md

@@ -12,6 +12,11 @@
 
 于是乎，TimeTunnel 命令就诞生了。
 
+## 注意事项
+
+* tt 命令的实现是：把函数的入参/返回值等，保存到一个`Map<Integer, TimeFragment>`里，默认的大小是 100。
+* tt 相关功能在使用完之后，需要手动释放内存，否则长时间可能导致OOM。退出 arthas 不会自动清除 tt 的缓存 map。
+
 ## 使用参考
 
 ### 启动 Demo
@@ -238,3 +243,16 @@ Affect(class count: 1 , method count: 1) cost in 56 ms, listenerId: 1
   2. **引用的对象**
 
      需要强调的是，`tt` 命令是将当前环境的对象引用保存起来，但仅仅也只能保存一个引用而已。如果方法内部对入参进行了变更，或者返回的对象经过了后续的处理，那么在 `tt` 查看的时候将无法看到当时最准确的值。这也是为什么 `watch` 命令存在的意义。
+
+
+### 通过索引删除指定的 tt 记录
+
+```
+tt -d 1001
+```
+
+### 清除所有的 tt 记录
+
+```
+tt --delete-all
+```

site/docs/en/doc/tt.md

@@ -10,6 +10,11 @@ In such difficulties, `tt` comes into play.
 
 With the help of `tt` (_TimeTunnel_), you can check the contexts of the methods at different times in execution history.
 
+## Precautions
+
+* The implementation of the tt command is to save the input parameters/return values of the function into a `Map<Integer, TimeFragment>`. The default size is 100.
+* After using tt related functions, you need to manually release the memory, otherwise OOM may occur for a long time. Exiting arthas will not automatically clear tt's cache map.
+
 ## Usage
 
 ### Start Demo
@@ -210,3 +215,15 @@ F.Y.I
 2. params may be modified
 
    Arthas save params into an array, they are object references. The Objects may be modified by other code.
+
+### Delete the specified tt record by index
+
+```
+tt -d 1001
+```
+
+### Clear all tt records
+
+```
+tt --delete-all
+```