update doc

doc/BASIC_KNOWLEDGE.md

@@ -26,7 +26,7 @@ The are four built-in types  of  `WeChatImage` in `fluwx`:
   WeChatImage.binary(Uint8List source, {String suffix = ".jpeg"});
 ```
 
-The suffix shall begins with `.`. The priority of `suffix` is highest, `fluwx` will try to read suffix from paths if `suffix` is blank.
+The priority of `suffix` is highest, `fluwx` will try to read suffix from paths if `suffix` is blank.
 
 The max size of image youcan share to WeChat is `10M`.`Fluwx` wil compress `WeChatImage` itself if it's  used as `thumbnail` or `hdImagePath`,  
 otherwise, it doesn't. However, you'd better compress thumbnail yourself as the result of compression is unpredictable.

doc/BASIC_KNOWLEDGE_CN.md

@@ -26,7 +26,7 @@
   WeChatImage.binary(Uint8List source, {String suffix = ".jpeg"});
 ```
 
-其中， `suffix` 应该以`.`开头. `suffix` 优先级最高, 如果`suffix`是空白的，`fluwx` 将会尝试从文件路径中读取后缀.
+其中， `suffix` 优先级最高, 如果`suffix`是空白的，`fluwx` 将会尝试从文件路径中读取后缀.
 
 在分享图片的功能，图片不能超过`10M`.如果图片被用作`thumbnail` 或 `hdImagePath`，`Fluwx` 会对 `WeChatImage` 进行压缩,  
 否则不会压缩. 但是，最好还是自己压缩，因为不保证`fluwx`压缩效果。