docs: add iluwatar as a contributor (#1343)

* docs: update README.md [skip ci]

* docs: create .all-contributorsrc [skip ci]

Co-authored-by: allcontributors[bot] <46447321+allcontributors[bot]@users.noreply.github.com>

.all-contributorsrc

@@ -0,0 +1,24 @@
+{
+  "files": [
+    "README.md"
+  ],
+  "imageSize": 100,
+  "commit": false,
+  "contributors": [
+    {
+      "login": "iluwatar",
+      "name": "Ilkka Seppälä",
+      "avatar_url": "https://avatars1.githubusercontent.com/u/582346?v=4",
+      "profile": "https://github.com/iluwatar",
+      "contributions": [
+        "code"
+      ]
+    }
+  ],
+  "contributorsPerLine": 7,
+  "projectName": "java-design-patterns",
+  "projectOwner": "iluwatar",
+  "repoType": "github",
+  "repoHost": "https://github.com",
+  "skipCi": true
+}

README.md

@@ -1,4 +1,7 @@
 <!-- the line below needs to be an empty line C: (its because kramdown isnt
+<!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
+[![All Contributors](https://img.shields.io/badge/all_contributors-1-orange.svg?style=flat-square)](#contributors-)
+<!-- ALL-CONTRIBUTORS-BADGE:END -->
      that smart and dearly wants an empty line before a heading to be able to
      display it as such, e.g. website) -->
 
@@ -58,3 +61,22 @@ you and answer your questions in the [Gitter chatroom](https://gitter.im/iluwata
 # License
 
 This project is licensed under the terms of the MIT license.
+
+## Contributors ✨
+
+Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/docs/en/emoji-key)):
+
+<!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section -->
+<!-- prettier-ignore-start -->
+<!-- markdownlint-disable -->
+<table>
+  <tr>
+    <td align="center"><a href="https://github.com/iluwatar"><img src="https://avatars1.githubusercontent.com/u/582346?v=4" width="100px;" alt=""/><br /><sub><b>Ilkka Seppälä</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=iluwatar" title="Code">💻</a></td>
+  </tr>
+</table>
+
+<!-- markdownlint-enable -->
+<!-- prettier-ignore-end -->
+<!-- ALL-CONTRIBUTORS-LIST:END -->
+
+This project follows the [all-contributors](https://github.com/all-contributors/all-contributors) specification. Contributions of any kind welcome!