message: add detail regarding manual mocks and node modules
diff: @@ -29,7 +29,7 @@ directory as the ``node_modules`` folder. Eg:
  config
  ```
  -When a manual mock exists for a given module, Jest's module system will use that module when explicitly calling `jest.mock('moduleName')`.
  +When a manual mock exists for a given module, Jest's module system will use that module when explicitly calling `jest.mock('moduleName')`. However, manual mocks will take precedence over node modules even if `jest.mock('moduleName')` is not called. To opt out of this behavior you will need to explicitly call `jest.unmock('moduleName')` in tests that should use the actual module implementation.
  Here's a contrived example where we have a module that provides a summary of
  all the files in a given directory.
  