Add description for api

docs/layers/api.md

@@ -1,3 +1,19 @@
 # API
 
 Is a decoupled layer of interfaces to data and/or functionality of one or more components.
+
+## CircleAPI.jsx
+
+We provided some functions for doing some procedures on user circles.
+
+```javascript
+getUserBelongCircles = (circles,followingId) => {}
+```
+
+To get circles which the user is added in. `circles` is the parameter that we want to know if user is exist in any of them or not. `followingId` is the parameter that show the use identifier who we are looking for in `circles` parameter.
+
+```javascript
+getFollowingUsers = (circles) => {}
+```
+
+Get the user who are in circles. `circles` is the paramater that we get users from.