Update CONTRIBUTING.md

Clarify why the linter needs to run on *built* Enzyme, in order to pass fully.

Author: jack-lewin

CONTRIBUTING.md

@@ -74,9 +74,9 @@ npm run test:watch
 This codebase adheres to the [Airbnb Styleguide](https://github.com/airbnb/javascript) and is
 enforced using [ESLint](http://eslint.org/).
 
-As with the test suite, linting rules apply to *built* Enzyme.
+As with the test suite, the linter will not fully pass unless it is running on *built* Enzyme. This is because the ESLint `import/*` rules rely on finding the target files in the filesystem (which won't be there unless they've been built).
 
-It is recommended that you install an eslint plugin for your editor of choice when working on this
+It is recommended that you install an ESLint plugin for your editor of choice when working on this
 codebase, however you can always check to see if the source code is compliant by running:
 
 ```bash