Add Set doc (#128)

Add <Set /> documentation

Author: denisborovikov

docs/components/Set.md

@@ -1,5 +1,53 @@
 # Set
 
-// TODO: :disappointed_relieved:
+The Set component is used to work with an array of unique values.
 
-Send us a PR if you want to collaborate! :green_heart:
+```js
+import { Set } from 'react-powerplug'
+```
+
+```jsx
+<Set initial={['react', 'babel']}>
+  {({ values, remove, add }) => (
+    <TagManager>
+      <FormInput onSubmit={add} />
+      {values.map(tag => (
+        <Tag onRemove={() => remove(tag)}>{tag}</Tag>
+      ))}
+    </TagManager>
+  )}
+</Set>
+```
+
+## Set Props
+
+**initial = []** _(optional)_  
+Specifies the initial values state, must be an array. Duplicate items will be removed. 
+By default, the initial values state is an empty array.
+
+**onChange** _(optional)_  
+The onChange event of the Set is called whenever the values state changes.
+
+## Set Children Props
+
+TL;DR: `{ values, add, clear, remove, has }`
+
+**values**  
+`array`  
+Your values state, contains only unique items
+
+**add**  
+`(value: any) => void`  
+Add a unique `value` to your values array. Does nothing if values array already includes a `value`.
+
+**clear**
+`() => any`  
+Reset values state to an empty array
+
+**remove**  
+`(value: any) => void`  
+Remove a `value` from your values array
+
+**has**  
+`(value: any) => boolean`  
+True if values array includes a `value`