help: update template examples to use reST literal syntax

This should prevent processing backslashes as reST syntax elements. Before
this patch, '\' was lost in HTML and man pages.

mercurial/help/templates.txt

@@ -43,13 +43,13 b' In addition to filters, there are some b'
 
 .. functionsmarker
 
-Also, for any expression that returns a list, there is a list operator:
+Also, for any expression that returns a list, there is a list operator::
 
-- expr % "{template}"
+    expr % "{template}"
 
-As seen in the above example, "{template}" is interpreted as a template.
-To prevent it from being interpreted, you can use an escape character "\{"
-or a raw string prefix, "r'...'".
+As seen in the above example, ``{template}`` is interpreted as a template.
+To prevent it from being interpreted, you can use an escape character ``\{``
+or a raw string prefix, ``r'...'``.
 
 Some sample command line templates: