Create a PR template (#515)

Created a baseline PR template for contributors to describe their changes via a uniform submission form.

Author: DellaBitta

.github/PULL_REQUEST_TEMPLATE/pull_request_template.md

@@ -0,0 +1,23 @@
+### Description
+> Provide details of the change, and generalize the change in the PR title above.
+
+[replace this line]: # (Describe your changes in detail.)
+***
+### Testing
+> Describe how you've tested these changes. Link any manually triggered `Integration tests` or `CPP binary SDK Packaging` Github Action workflows, if applicable.
+
+
+[replace this line]: # (Describe your testing in detail.)
+***
+
+### Type of Change
+Place an `x` the applicable box:
+- [ ] Bug fix. Add the issue # below if applicable.
+- [ ] New feature. A non-breaking change which adds functionality.
+- [ ] Other, such as a build process or documentation change.
+***
+
+#### Notes
+- Bug fixes and feature changes require an update to the `Release Notes` section of `release_build_files/readme.md`.
+- Read the contribution guidelines [CONTRIBUTING.md](https://github.com/firebase/firebase-cpp-sdk/blob/main/CONTRIBUTING.md).
+- Changes to the public API require an internal API review. If you'd like to help us make Firebase APIs better, please propose your change in a feature request so that we can discuss it together.