Update README.md to increase visibility of deprecation note (#10)

* Update README.md to increase visibility of deprecation note

---------

Co-authored-by: Brad Broge <84735131+bradbroge@users.noreply.github.com>

Author: esmitperez

README.md

@@ -4,7 +4,8 @@
 
 # spreedly-android
 
-Not actively maintained at this time. Contact Support with questions.
+> # **Warning**
+> Not actively maintained at this time. Contact Support with questions.
 
 # Integration
 All integration options require a Spreedly account and an environment key. See [Create Your API Credentials](https://docs.spreedly.com/basics/credentials/#environment-key) for details.