Updating README.md with PHP runtime requirement

Author: naneau

README.md

@@ -8,7 +8,7 @@ This library was written out of the need to obfuscate the source for a private l
 
 While this tool does not make PHP code impossible to read, it will make it significantly less legible.
 
-It is compatible with PHP up to and including 5.5.
+It is compatible with PHP 5.3, 5.4 and 5.5, but needs PHP 5.4+ to run.
 
 ## Usage