chore: add links to more sample of code (#104)

* add links to more sample of code

* Update API.md

* Update API.md

Author: enieber

docs/API.md

@@ -5,7 +5,9 @@ title: API
 
 This page gathers public API of `react-native-testing-library` along with usage examples.
 
-## `render`
+## `render` 
+
+- [`Example code`](https://github.com/callstack/react-native-testing-library/blob/master/src/__tests__/render.test.js)
 
 Defined as:
 
@@ -135,6 +137,8 @@ Get the rendered component JSON representation, e.g. for snapshot testing.
 
 ## `shallow`
 
+- [`Example code`](https://github.com/callstack/react-native-testing-library/blob/master/src/__tests__/shallow.test.js)
+
 Shallowly renders given React component. Since it doesn't return helpers to query the output, it's mostly advised to used for snapshot testing (short snapshots are best for code reviewers).
 
 ```jsx
@@ -148,6 +152,8 @@ test('Component has a structure', () => {
 
 ## `fireEvent`
 
+- [`Example code`](https://github.com/callstack/react-native-testing-library/blob/master/src/__tests__/fireEvent.test.js)
+
 Invokes a given event handler (whether native or custom) on the element, bubbling to the root of the rendered tree. The three most common events (`press`, `changeText`, and `scroll`) have been aliased for convenience.
 
 ### `fireEvent: (element: ReactTestInstance, eventName: string, data?: *) => void`
@@ -252,6 +258,8 @@ fireEvent.scroll(getByTestId('scroll-view'), eventData);
 
 ## `waitForElement`
 
+- [`Example code`](https://github.com/callstack/react-native-testing-library/blob/master/src/__tests__/waitForElement.test.js)
+
 Defined as:
 
 ```jsx
@@ -278,6 +286,8 @@ If you're using Jest's [Timer Mocks](https://jestjs.io/docs/en/timer-mocks#docsN
 
 ## `debug`
 
+- [`Example code`](https://github.com/callstack/react-native-testing-library/blob/master/src/__tests__/debug.test.js)
+
 Log prettified shallowly rendered component or test instance (just like snapshot) to stdout.
 
 ```jsx