Added links to Measurement Protocol and php-gacx to README.md

Author: thomasbachem

README.md

@@ -6,10 +6,14 @@ where it has 8,000+ downloads and 160+ stares.
 
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 **NOTE:** php-ga is no longer maintained as Google finally released an official server-side
-tracking API: Measurement Protocol! I couldn't find any well-implemented client library for
-PHP yet, so feel free to help make php-ga 2.0 a Measurement Protocol PHP client library.
+tracking API: [Measurement Protocol](https://developers.google.com/analytics/devguides/collection/protocol/v1/)!
+I couldn't find any well-implemented client library for PHP yet, so feel free to help make
+php-ga 2.0 a Measurement Protocol PHP client library.
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+You might also be interested in the companion project [php-gacx](https://github.com/thomasbachem/php-gacx)
+for Google Analytics Content Experiments.
+
 
 About
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@@ -128,4 +132,4 @@ Thanks to Matt Clarke for two great articles/tutorials:
 Disclaimer
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-Google Analytics is a registered trademark of Google Inc.
+Google Analytics is a registered trademark of Google Inc.