Add docs for addReduce function

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

docs/functions/addReduce.md

@@ -0,0 +1,62 @@
+# Flux Query Builder Docs
+
+## Functions » addReduce()
+
+### Parameters:
+
+<table>
+  <tbody>
+    <tr>
+      <th>Name</th>
+      <th>Required</th>
+      <th>Data type</th>
+      <th>Description</th>
+    </tr>
+    <tr>
+      <td>settings</td>
+      <td>Yes</td>
+      <td>array</td>
+      <td>
+        Reducer calculation to apply to each row record.
+      </td>
+    </tr>
+    <tr>
+      <td>identity</td>
+      <td>Yes</td>
+      <td>array</td>
+      <td>Record that defines the reducer record and provides initial values for the reducer operation on the first row.</td>
+    </tr>
+  </tbody>
+</table>
+
+
+### Example
+
+```php
+use Arendsen\FluxQueryBuilder\Type\MathType;
+```
+
+```php
+->addReduce([
+  [
+    'count' => new MathType('accumulator.count + 1'),
+  ],
+  [
+    'count' => 0,
+  ]
+])
+```
+
+This will result in the following Flux function part:
+
+```
+|> reduce(fn: (r, accumulator) => ({
+    sum: r._value + accumulator.sum
+  }), 
+  identity: {sum: 0}
+)
+```
+
+### Extra resources
+
+* [Flux documentation](https://docs.influxdata.com/flux/v0.x/stdlib/universe/reduce/)