Update chapters/annotations.tex

write out underscore

Co-Authored-By: Thomas Beutlich <modelica@tbeu.de>

chapters/annotations.tex

@@ -836,7 +836,7 @@ \subsubsection{Text}\doublelabel{text}
 
 There are a number of common macros that can be used in the text, and
 they should be replaced when displaying the text as follows (in order such that the earliest ones have precedence,
-and using the longest sequence of identifier characters - alphanumeric and \_):
+and using the longest sequence of identifier characters - alphanumeric and underscore):
 
 \begin{itemize}
 \item