[add] add description to readme

Author: akakou

README.md

@@ -1,2 +1,31 @@
 # round-robin
 This module makes round-robin strings.
+
+## Usage
+### Installation
+  This module has no installer yet, so you can install only yourself.
+### Specification
+#### Constructor Arguments
+| name               | type | description                                                   |
+| ------------------ |:----:| --------------------------------------------------------------|
+| any_characters     | list | This list consolidate to character_list.                      |
+| use_all            | bool | If it has True,  character_list has all aphabets and numbers. |
+| use_aphabets       | bool | If it has True,  character_list has all aphabets.             |
+| use_small_aphabets | bool | If it has True, character_list has smaller aphabets.          |
+| use_large_aphabets | bool | If it has True, character_list has larger aphabets.           |
+| use_numbers        | bool | If it has True, character_list has all numbers.               |
+
+
+### Example
+This program continue getting round_robin strings from RoundRobin.next() and printing them.
+
+  ```python
+  import round_robin
+  import time
+  
+  roundrobin = round_robin.RoundRobin(use_all=True)
+  
+  for pattern in roundrobin.next():
+    print(pattern)
+    time.sleep(0.1)
+  ```