Update rulesets-commit-regex.md (#55360)

Co-authored-by: Copilot <[email protected]>

Author: patrick-knight

data/reusables/repositories/rulesets-commit-regex.md

@@ -6,6 +6,8 @@ Rulesets support RE2 syntax. For more information, see Google's [syntax guide](h
 
 By default, regular expressions in metadata restrictions do not consider multiple lines of text. For example, if you have a multiline commit message, the pattern `^ABC` will be a match if the first line of the message starts with `ABC`. To match multiple lines of the message, start your expression with `(?m)`.
 
+When using regular expression metacharacter classes that contain a backslash `\` it must be escaped with an additional backslash. For example `task#\\d{1,4}`
+
 The negative lookahead assertion, denoted `?!`, is not supported. However, for cases where you need to look for a given string that is not followed by another given string, you can use the positive lookahead assertion, denoted `?`, combined with the "Must not match a given regex pattern" requirement.
 
 > [!NOTE]