Add Codecov badge to README.md

Author: wzieba

README.md

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 # Parsely Android SDK
 
-[![Maven Central](https://img.shields.io/maven-central/v/com.parsely/parsely.svg?label=Maven%20Central)](https://central.sonatype.com/artifact/com.parsely/parsely) [![Assemble project](https://github.com/Parsely/parsely-android/actions/workflows/readme.yml/badge.svg)](https://github.com/Parsely/parsely-android/actions/workflows/readme.yml)
+[![Maven Central](https://img.shields.io/maven-central/v/com.parsely/parsely.svg?label=Maven%20Central)](https://central.sonatype.com/artifact/com.parsely/parsely) [![Assemble project](https://github.com/Parsely/parsely-android/actions/workflows/readme.yml/badge.svg)](https://github.com/Parsely/parsely-android/actions/workflows/readme.yml) [![codecov](https://codecov.io/gh/Parsely/parsely-android/graph/badge.svg?token=M7PNYbYvKP)](https://codecov.io/gh/Parsely/parsely-android)
 
 The Parse.ly Android SDK is a Java library providing Parse.ly tracking functionality to native
 Android apps. Like any other framework you might include in your project, the Parse.ly SDK provides