Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -5,6 +5,8 @@ agree to a Contributor License Agreement (CLA) declaring that you have the right
 and actually do, grant us the rights to use your contribution. For details, visit
 https://cla.microsoft.com.
 
+> Important: when translating text in this repo, please ensure that you do not use machine translation. We will verify translations via the community, so please only volunteer for translations in languages where you are proficient.
+
 When you submit a pull request, a CLA-bot will automatically determine whether you need
 to provide a CLA and decorate the PR appropriately (e.g., label, comment). Simply follow the
 instructions provided by the bot. You will only need to do this once across all repositories using our CLA.