docs(shortcut): add paste shortcut key

Author: marjune163

README.md

@@ -283,3 +283,4 @@ server [options]
 - `Ctrl`/`Opt` + `↓`: move focus to last file item
 - Repeat inputting same character will look for next file that prefixes with it.
 - Non-repeat inputs will be remembered as a string in short time to look for next file prefix match.
+- When upload is enabled, pasting(`Ctrl`/`Cmd` + `v`) image or text content will upload that content as a file.

README.zh-CN.md

@@ -281,3 +281,4 @@ server [选项]
 - `Ctrl`/`Opt` + `↓`：把焦点移动到最后一个文件项
 - 重复输入相同字符将查找下一个前缀匹配该字符的文件。
 - 输入不重复的字符，将在短时间内被记忆为字符串，用于查找下一个前缀匹配的文件。
+- 当已启用上传时，粘贴（`Ctrl`/`Cmd` + `v`）图像或文本会将此内容上传为文件。