Added usage instructions to readme

Author: betterphp

README.md

@@ -1,2 +1,17 @@
 # Datacode PHP Code Standard
 This repo contains the phpcs ruleset used by all of our other PHP projects.
+
+The package should be included by composer
+```
+{
+    "require": {
+        "datacodetech/phpcs-ruleset": "^2.0.0"
+    }
+}
+```
+Then references in the `ruleset.xml` file for the project
+```
+<ruleset>
+    <rule ref="vendor/datacodetech/phpcs-ruleset/DatacodeStandard" />
+</ruleset>
+```