Clarifies cleanup docs for Vue and Preact

Author: kyle-n

docs/preact-testing-library/api.mdx

@@ -52,9 +52,11 @@ const {results} = render(<YourComponent />, {options})
 
 Unmounts the component from the container and destroys the container.
 
-📝 When you import anything from the library, this automatically runs after each
-test. If you'd like to disable this then set `process.env.PTL_SKIP_AUTO_CLEANUP`
-to true when running your tests.
+> This is called automatically if your testing framework (such as mocha, Jest or
+> Jasmine) injects a global `afterEach()` function into the testing environment.
+
+If you'd like to disable this then set `process.env.PTL_SKIP_AUTO_CLEANUP` to
+true when running your tests.
 
 ```jsx
 import {render, cleanup} from '@testing-library/preact'

docs/vue-testing-library/api.mdx

@@ -232,9 +232,8 @@ See a working example of `update` in the
 Unmounts Vue trees that were mounted with
 [render](#rendercomponent-options-callback).
 
-> If you are using an environment that supports `afterEach` hook (as in Jest),
-> there's no need to call `cleanup` manually. Vue Testing Library handles it for
-> you.
+> This is called automatically if your testing framework (such as mocha, Jest or
+> Jasmine) injects a global `afterEach()` function into the testing environment.
 
 Failing to call `cleanup` when you've called `render` could result in a memory
 leak and tests which are not idempotent (which can lead to difficult to debug