Update markdown.md example with asterisks and underscores for clarity

doc/user/markdown.md

@@ -431,7 +431,7 @@ Emphasis, aka italics, with *asterisks* or _underscores_.
 
 Strong emphasis, aka bold, with **asterisks** or __underscores__.
 
-Combined emphasis with **asterisks and _underscores_**.
+Combined emphasis with **_asterisks and underscores_**.
 
 Strikethrough uses two tildes. ~~Scratch this.~~
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