chore: tidy up OSS files (#186)

Author: wangela

.github/snippet-bot.yml

@@ -0,0 +1 @@
+alwaysCreateStatusCheck: true

CODEOWNERS

@@ -14,4 +14,4 @@
 
 # https://help.github.com/en/github/creating-cloning-and-archiving-repositories/about-code-owners
 
-.github/ @googlemaps/admin
+.github/ @googlemaps-samples/devrel-admin

CONTRIBUTING.md

@@ -0,0 +1,35 @@
+# Not accepting contributions
+
+Since this repository is a one-way mirror of the code from `pod try sync` we are
+not currently accepting external contributions. Pull requests are accepted from
+a limited set of repository members.
+
+## If you are contributing
+
+### Sign our Contributor License Agreement
+
+Contributions to this project must be accompanied by a
+[Contributor License Agreement](https://cla.developers.google.com/about) (CLA).
+You (or your employer) retain the copyright to your contribution; this simply
+gives us permission to use and redistribute your contributions as part of the
+project.
+
+If you or your current employer have already signed the Google CLA (even if it
+was for a different project), you probably don't need to do it again.
+
+Visit <https://cla.developers.google.com/> to see your current agreements or to
+sign a new one.
+
+### Review our community guidelines
+
+This project follows
+[Google's Open Source Community Guidelines](https://opensource.google/conduct/).
+
+## Contribution process
+
+### Code reviews
+
+All submissions, including submissions by project members, require review. We
+use GitHub pull requests for this purpose. Consult
+[GitHub Help](https://help.github.com/articles/about-pull-requests/) for more
+information on using pull requests.