Add docs for addRawFunction function

Signed-off-by: David Arendsen <darendsen@gamepoint.com>

docs/functions/addRawFunction.md

@@ -0,0 +1,33 @@
+# Flux Query Builder Docs
+
+## Functions » addRawFunction()
+
+### Parameters:
+
+<table>
+  <tbody>
+    <tr>
+      <th>Name</th>
+      <th>Data type</th>
+      <th>Description</th>
+    </tr>
+    <tr>
+      <td>input</td>
+      <td>string</td>
+      <td>Insert any Flux function here.</td>
+    </tr>
+  </tbody>
+</table>
+
+
+### Example
+
+```php
+->addRawFunction('|> aggregateWindow(every: 20s, fn: mean, timeDst: "_time")')
+```
+
+This will result in the following Flux function part:
+
+```
+|> aggregateWindow(every: 20s, fn: mean, timeDst: "_time")
+```