Add --type={repo,vendor} to README and configuration test (#1496)

Follow-up to https://github.com/bazel-contrib/buildtools/pull/1485.

## Buildtools PR checklist

- [x] The code in this PR is covered by unit/integration tests.
- [x] I have tested these changes and provide testing instructions
below.
- [x] I have either responded to, or resolved all Gemini comments on the
PR.
- [x] I have read Google Eng Practices on [Small
Changes](https://google.github.io/eng-practices/review/developer/small-cls.html),
this PR either follows these guidelines or the description provides
reasoning for why they can not be followed.

buildifier/README.md

diff --git a/buildifier/README.md b/buildifier/README.md
index faef977..82ff565 100644
--- a/buildifier/README.md
+++ b/buildifier/README.md
@@ -55,6 +55,8 @@
 cat foo.bar | buildifier --type=workspace
 cat foo.bar | buildifier --type=default
 cat foo.bar | buildifier --type=module
+cat foo.bar | buildifier --type=repo
+cat foo.bar | buildifier --type=vendor
 ```
 
 ## Linter

buildifier/config/config_test.go

diff --git a/buildifier/config/config_test.go b/buildifier/config/config_test.go
index ca31dd6..9b5264d 100644
--- a/buildifier/config/config_test.go
+++ b/buildifier/config/config_test.go
@@ -265,6 +265,8 @@
 		"type workspace":        {options: "--type=workspace"},
 		"type default":          {options: "--type=default"},
 		"type module":           {options: "--type=module"},
+		"type repo":             {options: "--type=repo"},
+		"type vendor":           {options: "--type=vendor"},
 		"type auto":             {options: "--type=auto"},
 		"type error":            {options: "--type=foo", wantErr: fmt.Errorf("unrecognized input type foo; valid types are build, bzl, workspace, default, module, repo, vendor, auto")},
 		"warnings all": {options: "--warnings=all", wantWarnings: []string{