Merge pull request #2116 from SEKOIA-IO/regex_additional_info

add syntax info about the regex we support

docs/xdr/features/detect/sigma.md

@@ -72,7 +72,7 @@ Here is the list of supported modifiers:
 - `base64`: match the value encoded with Base64
 - `endswith`: the value is expected at the end of the field's content (replaces e.g. `*\cmd.exe`)
 - `startswith`: the value is expected at the beginning of the field's content. (replaces e.g. `adm*`)
-- `re`: the value is a regular expression. Regular expressions are case sensitive by default
+- `re`: the value is a [regular expression](https://github.com/andreasvc/pyre2). Regular expressions are case sensitive by default
 - `cidr`: the value is a subnet in CIDR notation (e.g. `192.168.1.0/24`) the IP address should belong to
 - `lt`: less than this value
 - `lte`: less than or equal to this value