Documentation: filter-branch: show --ignore-unmatch in main index-filter example

Rearrange the example usage of

  git filter-branch --index-filter 'git rm --cached ...'

so that --ignore-unmatch is in the main example block.  People keep
stumbling over the (lack of this) option to the point where it is a
FAQ, so we would want to expose the most common usage where it stands
out.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-filter-branch.txt

@@ -91,7 +91,9 @@ OPTIONS
 --index-filter <command>::
 	This is the filter for rewriting the index.  It is similar to the
 	tree filter but does not check out the tree, which makes it much
-	faster.  For hairy cases, see linkgit:git-update-index[1].
+	faster.  Frequently used with `git rm \--cached
+	\--ignore-unmatch ...`, see EXAMPLES below.  For hairy
+	cases, see linkgit:git-update-index[1].
 
 --parent-filter <command>::
 	This is the filter for rewriting the commit's parent list.
@@ -204,19 +206,18 @@ However, if the file is absent from the tree of some commit,
 a simple `rm filename` will fail for that tree and commit.
 Thus you may instead want to use `rm -f filename` as the script.
 
-A significantly faster version:
+Using `\--index-filter` with 'git-rm' yields a significantly faster
+version.  Like with using `rm filename`, `git rm --cached filename`
+will fail if the file is absent from the tree of a commit.  If you
+want to "completely forget" a file, it does not matter when it entered
+history, so we also add `\--ignore-unmatch`:
 
 --------------------------------------------------------------------------
-git filter-branch --index-filter 'git rm --cached filename' HEAD
+git filter-branch --index-filter 'git rm --cached --ignore-unmatch filename' HEAD
 --------------------------------------------------------------------------
 
 Now, you will get the rewritten history saved in HEAD.
 
-As with using `rm filename`, `git rm --cached filename` will fail
-if the file is absent from the tree of a commit.  If it is not important
-whether the file is already absent from the tree, you can use
-`git rm --cached --ignore-unmatch filename` instead.
-
 To rewrite the repository to look as if `foodir/` had been its project
 root, and discard all other history: