change README

Author: nomikura

README.md

@@ -1,4 +1,5 @@
 # AtCoder API(informal)
+- [AtCoder](https://atcoder.jp/)の全コンテスト情報を取得できます
 
 ## [Contest](https://atcoder-api.appspot.com/contests)
 | Field            | Description                                                  |
@@ -7,4 +8,4 @@
 | title            | String. Contest title.                                       |
 | startTimeSeconds | Integer.Contest start time in unix format.                   |
 | durationSeconds  | Integer.Duration of the contest in seconds.                  |
-| ratedRange       | String. Contest rated range.                                 |
+| ratedRange       | String. Contest rated range.                                 |