Add Shields.io badges to readme (#11)

* Add Shields.io badges to readme

* Update demo badges

* Add default cache value

* Add rating to suggested use for CodeChef

* Add title to images

* Add angle brackets to suggested use

Author: k3KAW8Pnf7mkmdSMPHz27

README.md

@@ -7,9 +7,28 @@ https://competitive-coding-api.herokuapp.com/api/
 ## Request Format
 https://competitive-coding-api.herokuapp.com/api/{platform_name}/{user_name}
 
-### Example
+### Example URL
 https://competitive-coding-api.herokuapp.com/api/codechef/abhijeet_ar
 
+### Example Badges
+[Shields](https://shields.io/) can create dynamically updated badges from a JSON source such as this API. More configuration options are also available in their section on [dynamic badges](https://shields.io/#dynamic-badge).
+
+Replace `<USERNAME>` with your username on that platform.
+
+#### <a href="https://codeforces.com/profile/abhijeet_ar"><img src="https://img.shields.io/badge/dynamic/json?&color=1f8acb&logo=codeforces&label=Codeforces&url=https://competitive-coding-api.herokuapp.com/api/codeforces/abhijeet_ar&query=%24.rating&prefix=Rating%20&style=for-the-badge&cacheSeconds=259200" alt="abhijeet_ar's profile on Codeforces" title="abhijeet_ar's profile on Codeforces"></a>
+`https://img.shields.io/badge/dynamic/json?&color=1f8acb&logo=codeforces&label=Codeforces&url=https://competitive-coding-api.herokuapp.com/api/codeforces/<USERNAME>&query=%24.<FIELD>&prefix=<TEXT>&style=for-the-badge&cacheSeconds=86400`
+
+Suggested use,
+* `<FIELD>` = `rating`
+* `<TEXT>` = `Rating%20`
+
+#### <a href="https://www.codechef.com/users/radix28_numb"><img src="https://img.shields.io/badge/dynamic/json?label=CodeChef&query=%24.country_rank&url=https://competitive-coding-api.herokuapp.com/api/codechef/radix28_numb&prefix=US%20%23&logo=codechef&logoColor=f5f5dc&labelColor=7b5e47&style=for-the-badge&cacheSeconds=259200" alt="radix28_numb's profile on CodeChef" title="radix28_numb's profile on CodeChef"></a>
+`https://img.shields.io/badge/dynamic/json?label=CodeChef&query=%24.global_rank&url=https://competitive-coding-api.herokuapp.com/api/codechef/<USERNAME>&prefix=<TEXT>&logo=codechef&logoColor=f5f5dc&labelColor=7b5e47&style=for-the-badge&cacheSeconds=86400`
+
+Suggested use,
+* `<FIELD>` = `global_rank`, `country_rank` or `rating`
+* `<TEXT>` = `Rank%20`, country abbreviation (e.g., `US%20%23`) or `Rating%20`
+
 ### Pro Tip 💡
 Use this [JSON Formatter Chrome Extension](https://chrome.google.com/webstore/detail/json-formatter/bcjindcccaagfpapjjmafapmmgkkhgoa?hl=en) to view in a structured format.