Update app icon & add acknowledgements

Author: addyosmani

README.md

@@ -49,3 +49,7 @@ http://www.apache.org/licenses/LICENSE-2.0
 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
 
 Please note: this is not a Google product
+
+## Acknowledgements
+
+With thanks to Paul Lewis for his inspiration in the [Voice Memos](https://voice-memos.appspot.com/) app and [Yannick Lung](https://www.iconfinder.com/icons/315148/app_document_file_icon#size=512) for the App icon used.