Use pecl for installing

Author: bjori

docs/index.md

@@ -26,8 +26,7 @@ them using, for example, Composer.
 
 To build and install the driver:
 
-	$ wget https://github.com/10gen-labs/mongo-php-driver-prototype/releases/download/0.2.0/mongodb-0.2.0.tgz
-	$ pecl install mongodb-0.2.0.tgz
+	$ pecl install mongodb-alpha
 	$ echo "extension=mongodb.so" >> `php --ini | grep "Loaded Configuration" | sed -e "s|.*:\s*||"`