Added Readme Warning to prevent users to pull this version for now

Author: Geolim4

README.md

@@ -1,6 +1,12 @@
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 # Symfony 3 PhpFastCache Bundle
 
+#### :warning: Please note that the V3 is a major (BC breaking) update of the PhpFastCache Bundle !
+> As of the V3 the bundle is **absolutely** not compatible with previous versions.u the smoothest migration possible.
+One of the biggest change is the Phpfastcache's dependency which is not set to the v7 which it not backward compatible at all.
+Also please note that the bundle is currently in development and under a massive code rewrite.
+:warning: The code of the v3 is NOT production or development ready ATM.
+
 
 #### :thumbsup: Step 1: Include phpFastCache Bundle in your project with composer: