Fix quoting

lib/documentation/docs/help/en/Opening hours.md

@@ -104,7 +104,7 @@ The dialog allows you to set
 
 * __Name__ a descriptive name for the template.
 * __Default__ if checked this will be consider as a default template (typically further constrained by the other fields).
-* __Key__ the key this template is relevant for, if set to _Custom key_ you can add a non-standard value in the field below. The key values support SQL wild cards, that is _%_ matches zero or more characters, *_* matches a single character. Both wild card characters can be escaped with _\_ for literal matches.
+* __Key__ the key this template is relevant for, if set to _Custom key_ you can add a non-standard value in the field below. The key values support SQL wild cards, that is _%_ matches zero or more characters, *_* matches a single character. Both wild card characters can be escaped with _\\_ for literal matches.
 * __Region__ the region the template is applicable to.
 * __Object__ an application specific string to use for matching.