Added empty string error return in docs

Author: ErikPelli

bot.go

@@ -1069,6 +1069,7 @@ func (bot *BotAPI) SetMyCommands(commands []BotCommand) error {
 // EscapeText takes an input text and escape Telegram markup symbols.
 // In this way we can send a text without being afraid of having to escape the characters manually.
 // Note that you don't have to include the formatting style in the input text, or it will be escaped too.
+// If there is an error, an empty string will be returned.
 //
 // parseMode is the text formatting mode (ModeMarkdown, ModeMarkdownV2 or ModeHTML)
 // text is the input string that will be escaped