ci(copybara): set up Zuul to sync with dotfiles-external

GitOrigin-RevId: 5d313e1f2dd57b3c9c8ee317a545559ab9a16c8f
diff --git a/.copybara/README.md b/.copybara/README.md
index 4c57d54..c0e7a9c 100644
--- a/.copybara/README.md
+++ b/.copybara/README.md
@@ -4,11 +4,8 @@
 ## How to test the Copybara script
 
 1. Clone the private and public repos in your computer.
-2. Create a `test_repos_config.sky` file with the following contents:
-  ```sky
-test_origin_url = "file:///path/to/private/dotfiles"
-test_destination_url = "file:///path/to/dotfiles-external"
-```
+2. Create a `test_repos_config.bara.sky` based in the template
+`test_repos_config.bara.sky.template`.
 3. Run `sh export-commits-test.sh`.
 
 [copybara]: https://github.com/google/copybara
diff --git a/.copybara/test_repos_config.bara.sky.template b/.copybara/test_repos_config.bara.sky.template
new file mode 100644
index 0000000..1281fc2
--- /dev/null
+++ b/.copybara/test_repos_config.bara.sky.template
@@ -0,0 +1,2 @@
+test_origin_url = "file:///path/to/private/dotfiles"
+test_destination_url = "file:///path/to/dotfiles-external"