Merge branch 'nd/doc-git-index-version' into maint

Doc clean-up.

* nd/doc-git-index-version:
  git.txt: list index versions in plain English

Author: gitster

Documentation/git.txt

@@ -769,7 +769,8 @@ Git so take care if using Cogito etc.
 'GIT_INDEX_VERSION'::
 	This environment variable allows the specification of an index
 	version for new repositories.  It won't affect existing index
-	files.  By default index file version [23] is used.
+	files.  By default index file version 2 or 3 is used. See
+	linkgit:git-update-index[1] for more information.
 
 'GIT_OBJECT_DIRECTORY'::
 	If the object storage directory is specified via this