Update installation instructions

Author: alexott

README.md

@@ -15,10 +15,14 @@ __Note__: DataStax products do not support big-endian systems.
 ## Getting the Driver
 
 Binary versions of the driver, available for multiple operating systems and
-multiple versions of PHP, can be obtained from our [download server]. The
-source code is made available via [GitHub]. __If using [DataStax Enterprise]
+multiple versions of PHP, can be obtained from [DataStax download server]. The
+source code is made available via [GitHub]. __If you're using [DataStax Enterprise]
 use the [DSE PHP driver] instead__.
 
+__Note__: The driver extension is a wrapper around the 
+          [DataStax C/C++ Driver for Apache Cassandra] and is a requirement for proper
+          installation of the PHP extension binaries. Ensure these dependencies are met before proceeding.
+
 ## What's new in v1.2.0/v1.3.0
 
 * Support for [`duration`]