Review doc

Author: GromNaN

CONTRIBUTING.md

@@ -38,7 +38,8 @@ Before submitting a pull request:
 
 ## Run Tests
 
-The full test suite requires PHP cli with mongodb extension, a running MongoDB server.
+The full test suite requires PHP cli with mongodb extension and a running MongoDB server. A replica set is required for
+testing transactions.
 Duplicate the `phpunit.xml.dist` file to `phpunit.xml` and edit the environment variables to match your setup.
 
 ```bash
@@ -69,7 +70,8 @@ If the project maintainer has any additional requirements, you will find them li
 
 - **Add tests!** - Your patch won't be accepted if it doesn't have tests.
 
-- **Document any change in behaviour** - Make sure the documentation is kept up-to-date. Update the changelog for new features and bug fixes.
+- **Document any change in behaviour** - Make sure the documentation is kept up-to-date, and update the changelog for
+new features and bug fixes.
 
 - **Consider our release cycle** - We try to follow [SemVer v2.0.0](https://semver.org/). Randomly breaking public APIs is not an option.