feat(template): tracks Cargo's call-for-testing label

Author: weihanglo

draft/DRAFT_TEMPLATE

@@ -77,6 +77,8 @@ RFCs would benefit from user testing before moving forward:
 
 ### [Rustup](https://github.com/rust-lang/rustup/labels/call-for-testing)
 
+### [Cargo](https://github.com/rust-lang/cargo/labels/call-for-testing)
+
 If you are a feature implementer and would like your RFC to appear on the above list, add the new `call-for-testing`
 label to your RFC along with a comment providing testing instructions and/or guidance on which aspect(s) of the feature
 need testing.