patterns help: mention path full-match in intro

src/borg/archiver.py

@@ -1561,8 +1561,8 @@ class Archiver:
 
     helptext = collections.OrderedDict()
     helptext['patterns'] = textwrap.dedent('''
-        File patterns support four separate styles: fnmatch, shell, regular
-        expressions and path prefixes. By default, fnmatch is used for
+        File patterns support these styles: fnmatch, shell, regular expressions,
+        path prefixes and path full-matches. By default, fnmatch is used for
         `--exclude` patterns and shell-style is used for `--pattern`. If followed
         by a colon (':') the first two characters of a pattern are used as a
         style selector. Explicit style selection is necessary when a