Merge branch 'jc/grep-patterntype-default-doc'

Doc update.

* jc/grep-patterntype-default-doc:
  grep: clarify what `grep.patternType=default` means

Author: gitster

Documentation/config/grep.txt

@@ -8,7 +8,8 @@ grep.patternType::
 	Set the default matching behavior. Using a value of 'basic', 'extended',
 	'fixed', or 'perl' will enable the `--basic-regexp`, `--extended-regexp`,
 	`--fixed-strings`, or `--perl-regexp` option accordingly, while the
-	value 'default' will return to the default matching behavior.
+	value 'default' will use the `grep.extendedRegexp` option to choose
+	between 'basic' and 'extended'.
 
 grep.extendedRegexp::
 	If set to true, enable `--extended-regexp` option by default. This