Create checklist reference doc

Author: BenLloydPearson

plugins/filters/checklist/reference.md

@@ -0,0 +1,25 @@
+<a name="module_checklist"></a>
+
+## checklist
+Automatically check PRs against a checklist of conditions.
+This is useful if you want to ensure that PRs meet certain criteria before they can be merged.
+
+**Returns**: <code>string</code> - Returns a formatted GitHub comment with a checklist of conditions that the PR meets.  
+**License**: MIT  
+
+| Param | Type | Description |
+| --- | --- | --- |
+| Input | <code>string</code> | A blank string (no input variable is required) |
+| branch | <code>object</code> | The branch context variable. |
+| files | <code>object</code> | The files context variable. |
+| pr | <code>object</code> | The pr context variable. |
+| repo | <code>object</code> | The repo context variable. |
+| env | <code>object</code> | The env context variable. |
+| source | <code>object</code> | The source context variable. |
+
+**Example**  
+```js
+- action: add-comment@v1
+        args:
+        	comment: {{ "" | checklist(branch, files, pr, repo, env, source) }}
+```