chore: update CONTRIBUTING.md and add pull request template

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,10 @@
+Thank you for your interest in contributing! For general guidelines, please refer to
+the [contributing guide](https://github.com/GoogleCloudPlatform/app-gradle-plugin/blob/master/CONTRIBUTING.md).
+
+Before submitting a pull request, please make sure to:
+
+- [ ] Identify an existing [issue](https://github.com/GoogleCloudPlatform/app-gradle-plugin/issues) to associate
+  with your proposed change, or [file a new issue](https://github.com/GoogleCloudPlatform/app-gradle-plugin/issues/new).
+- [ ] Describe any implementation plans in the issue and wait for a review from the repository maintainers.
+
+Fixes #<issue_number_goes_here> 🛠️

CONTRIBUTING.md

@@ -1,18 +1,50 @@
-# Contributing to gcloud java wrapper
+Want to contribute? Great! First, read this page (including the small print at the end).
 
-The gcp gradle plugin is an open source project, we appreciate your help!
+## Before you contribute
 
-## Contributing code
+Before we can use your code, you must sign the
+[Google Individual Contributor License Agreement]
+(https://cla.developers.google.com/about/google-individual)
+(CLA), which you can do online. The CLA is necessary mainly because you own the
+copyright to your changes, even after your contribution becomes part of our
+codebase, so we need your permission to use and distribute your code. We also
+need to be sure of various other things—for instance that you'll tell us if you
+know that your code infringes on other people's patents. You don't have to sign
+the CLA until after you've submitted your code for review and a member has
+approved it, but you must do it before we can put your code into our codebase.
+Before you start working on a larger contribution, you should get in touch with
+us first through the issue tracker with your idea so that we can help out and
+possibly guide you. Coordinating up front makes it much easier to avoid
+frustration later on.
 
-1. First, please [sign either individual or corporate contributor license agreement](https://cla.developers.google.com/), whichever is applicable.
-2. Set your git user.email property to the address used for step 1. E.g.
+## Code reviews
+
+All submissions, including submissions by project members, require review. We
+use Github pull requests for this purpose.
+
+Before submitting a pull request, please make sure to:
+
+- Identify an existing [issue](https://github.com/GoogleCloudPlatform/app-gradle-plugin/issues) to associate with
+  your proposed change, or [file a new issue](https://github.com/GoogleCloudPlatform/app-gradle-plugin/issues/new).
+- Describe any implementation plans in the issue and wait for a review from the repository maintainers.
+
+### Typical Contribution Cycle
+
+1. Set your git user.email property to the address used for signing the CLA. E.g.
    ```
    git config --global user.email "janedoe@google.com"
    ```
    If you're a Googler or other corporate contributor,
    use your corporate email address here, not your personal address.
-3. Fork the repository into your own Github account.
-4. Please include unit tests for all new code.
-5. Check style and make sure all existing tests pass. (`./gradlew build`)
-6. Associate the change with an existing issue or file a [new issue](../../issues)
-7. Create a pull request!
+2. Fork the repository into your own Github account.
+3. Please include unit tests for all new code.
+4. Check style and make sure all existing tests pass. (`./gradlew build`)
+5. Associate the change with an existing issue or file a [new issue](../../issues)
+6. Create a pull request!
+
+## The small print
+
+Contributions made by corporations are covered by a different agreement than
+the one above, the
+[Software Grant and Corporate Contributor License Agreement]
+(https://cla.developers.google.com/about/google-corporate).