docs(reactive): update toJS/markRaw docs

packages/reactive/docs/api/markRaw.md

@@ -4,6 +4,8 @@
 
 Mark any object or class prototype as never being hijacked by observable, priority is higher than markObservable
 
+Note: If you mark an object that is already observable with markRaw, then toJS will not convert it into a normal object
+
 ## Signature
 
 ```ts

packages/reactive/docs/api/markRaw.zh-CN.md

@@ -4,6 +4,8 @@
 
 标记任意一个对象或者类原型为永远不可被 observable 劫持，优先级比 markObservable 高
 
+注意：如果对一个已经是 observable 的对象标记 markRaw，那么 toJS，是不会将它转换成普通对象的
+
 ## 签名
 
 ```ts

packages/reactive/docs/api/toJS.md

@@ -4,6 +4,8 @@
 
 Deep recursion converts observable objects into ordinary JS objects
 
+Note: If you mark an object that is already observable with markRaw, then toJS will not convert it into a normal object
+
 ## Signature
 
 ```ts

packages/reactive/docs/api/toJS.zh-CN.md

@@ -4,6 +4,8 @@
 
 深度递归将 observable 对象转换成普通 JS 对象
 
+注意：如果对一个已经是 observable 的对象标记 markRaw，那么 toJS，是不会将它转换成普通对象的
+
 ## 签名
 
 ```ts