update README about MavenCentral (#369)

Author: jaeopt

README.md

@@ -22,8 +22,17 @@ up an Optimizely X project and start using the SDK.
 ### Installing the SDK
 To add the android-sdk and all modules to your project, include the following in your app's `build.gradle`:
 
+---
+**NOTE**
+
+[Bintray/JCenter will be shut down](https://jfrog.com/blog/into-the-sunset-bintray-jcenter-gocenter-and-chartcenter/). The publish repository has been migrated to MavenCentral for the SDK version 3.10.1 or later. Older versions will be available in JCenter until February 1st, 2022.
+
+---
+
+
 ```
 repositories {
+	mavenCentral()
   	jcenter()
 }