Update ManualMocks.md

A bit more explanation on the procedure of using and inviting manual mockups. There are both issues and SO questions coming from the confusion of how and when the mock should be called, and if it will be automatically called.

website/versioned_docs/version-26.x/ManualMocks.md

@@ -9,7 +9,7 @@ Manual mocks are used to stub out functionality with mock data. For example, ins
 
 Manual mocks are defined by writing a module in a `__mocks__/` subdirectory immediately adjacent to the module. For example, to mock a module called `user` in the `models` directory, create a file called `user.js` and put it in the `models/__mocks__` directory. Note that the `__mocks__` folder is case-sensitive, so naming the directory `__MOCKS__` will break on some systems.
 
-> When we require that module in our tests, explicitly calling `jest.mock('./moduleName')` is **required**.
+> When we require that module in our tests (meaning we want to use the manual mock instead of the real implementation), explicitly calling `jest.mock('./moduleName')` is **required**.
 
 ## Mocking Node modules