Added docs for pluckSingleValue.

Author: Hyperkid123

packages/react-renderer-demo/src/docs-components/pf3-select.md

@@ -1,3 +1,11 @@
+### Select
+
+There are some additional props for PF3 variant to match PF3 requirements.
+
+|prop name|type|default value|description|
+|---------|----|-------------|-----------|
+|pluckSingleValue|`bool`|`true`|If a value is an array, component will pick its first item and set it as a new value. This will override the value in state from `[2, 4, 5]` to `2` for example.|
+
 ### Async Select
 
 PF3 Select allows to load the options asynchronously.