chore(readme): Setup all-contributors (#254)

Adds @titozzz as a contributor for code, ideas, review, maintenance, test, doc, infra.

This was requested by Titozzz [in this comment](https://github.com/react-native-community/react-native-webview/pull/253#issuecomment-455609852)

.all-contributorsrc

+{
+  "projectName": "react-native-webview",
+  "projectOwner": "react-native-community",
+  "repoType": "github",
+  "repoHost": "https://github.com",
+  "files": [
+    "README.md"
+  ],
+  "imageSize": 100,
+  "commit": false,
+  "contributors": [
+    {
+      "login": "titozzz",
+      "name": "Thibault Malbranche",
+      "avatar_url": "https://avatars1.githubusercontent.com/u/6181446?v=4",
+      "profile": "https://twitter.com/titozzz",
+      "contributions": [
+        "code",
+        "ideas",
+        "review",
+        "maintenance",
+        "test",
+        "doc",
+        "infra"
+      ]
+    }
+  ],
+  "contributorsPerLine": 7
+}

README.md

 # React Native WebView - a Modern, Cross-Platform WebView for React Native
+[![All Contributors](https://img.shields.io/badge/all_contributors-1-orange.svg?style=flat-square)](#contributors)
 
 **React Native WebView** is a modern, well-supported, and cross-platform WebView for React Native. It is intended to be a replacement for the built-in WebView (which will be [removed from core](https://github.com/react-native-community/discussions-and-proposals/pull/3)).
 
 - [Thibault Malbranche](https://github.com/Titozzz) ([Twitter @titozzz](https://twitter.com/titozzz)) from [Brigad](https://brigad.co/about)
 - [Empyrical](https://github.com/empyrical) ([Twitter @empyrical](https://twitter.com/empyrical))
 
+## Contributors
+
+Thanks goes to these wonderful people ([emoji key](https://github.com/all-contributors/all-contributors#emoji-key)):
+
+<!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section -->
+<!-- prettier-ignore -->
+| [<img src="https://avatars1.githubusercontent.com/u/6181446?v=4" width="100px;" alt="Thibault Malbranche"/><br /><sub><b>Thibault Malbranche</b></sub>](https://twitter.com/titozzz)<br />[💻](https://github.com/react-native-community/react-native-webview/commits?author=titozzz "Code") [🤔](#ideas-titozzz "Ideas, Planning, & Feedback") [👀](#review-titozzz "Reviewed Pull Requests") [🚧](#maintenance-titozzz "Maintenance") [⚠️](https://github.com/react-native-community/react-native-webview/commits?author=titozzz "Tests") [📖](https://github.com/react-native-community/react-native-webview/commits?author=titozzz "Documentation") [🚇](#infra-titozzz "Infrastructure (Hosting, Build-Tools, etc)") |
+| :---: |
+<!-- ALL-CONTRIBUTORS-LIST:END -->
+
+This project follows the [all-contributors](https://github.com/all-contributors/all-contributors) specification. Contributions of any kind welcome!
+
 ## License
 
 MIT