Clarify outcome of the guideline

guidelines/markdown.md

 
  *  For IT-related texts, variable names, underscores, tool names,
     filenames are considered as "jargon", which falls into the typical
-    case for emphasized text.
+    case for emphasized text.  Therefore, use `*myvar*` or `*mytool*`.
 
  *  However, if the text is (or should be, by author's opinion)
     represented as code, backticks may be better choice.