basic 3rd party instructions added.

custom-plugins-setup.md

@@ -0,0 +1,28 @@
+# Installation
+
+Installing 3rd party plugins is straight forward and handled through composer. In the root folder of your phpci instance update the ```composer.json``` file to include the new plugins you require:
+
+```yaml
+"require": {
+   \\...
+   "meadsteve/example-phpci-plugin" : "dev-master",
+   \\...
+}
+```
+running ```composer update plugin-provider/plugin-package ``` will then download the plugin.
+
+# Usage
+
+Once a new plugin has been installed to phpci any project can make use of this plugin. The plugin is referenced in the ```phpci.yml``` as a full class name including namespaces:
+
+```yml
+setup:
+  test:
+  php_mess_detector:
+    allowed_warnings: 0
+  \meadsteve\PhpciPlugins\ExamplePlugin:
+    option_one: 2
+```
+
+# Extra dependency configuration
+//TODO: document ```pluginconfig.php``` in project root.