OCI8: MFH: (PECL #14219) Improve README

ext/oci8/README

@@ -1,6 +1,7 @@
 Installing OCI8
 ---------------
 
+0. Overview
 1. Common requirements.
 2. Installing as shared extension.
 3. Installing as statically compiled extension.
@@ -8,6 +9,18 @@ Installing OCI8
 5. Testing OCI8
 6. DRCP and FAN Support
 
+
+0. Overview
+-----------
+
+The OCI8 extension allows you to access Oracle databases.  It can be
+built using Oracle 9.2, 10.2 or 11.1 client libraries, and allows
+Oracle's standard cross-version connectivity.  It can be used with PHP
+versions 4.3.9 to 5.3.
+
+The OCI8 extension is not related to or used by PDO_OCI, the PHP Data
+Objects (PDO) extension for Oracle.
+
 1. Common requirements
 ----------------------