Update README.md

Author: ravhb

README.md

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+# fetch-leetcode-submission
+Help you to fetch your leetcode submissions.
+
+The script runs on Chrome, which means you don't need any running environment. Just install the Chrome.
+
+After runned it,  the browser will download a formatted markdown file. This is a generated file [**demo**](https://github.com/duteng/leetcode/blob/master/README.md).
+
+## How to use
+1. Using Chrome to open the [leetcode](http://leetcode.com), log in, then the redirect to the the [submission page](https://leetcode.com/submissions/#/1)
+2. Open the Chrome Developer Tools console tab.
+3. Paste the code in index.js in console, then press the Enter in keyboard.
+
+![fetch1](https://user-images.githubusercontent.com/1821507/48863702-336f9d00-ee05-11e8-9958-3c98a37568f0.gif)
+
+## Need to know
+1. The script will retry when the request failed. You don't have stop the script when some request failed with 400.
+(My experience is that a same request may failed more than 50 times. Just retry, it will succeed finally)
+2. You can customize the markdown template, header or footer. You also can dump a JSON file.
+3. If you wanna have a try, set `onlyFetchFirstPage = true`. If you wanna dump all, `onlyFetchFirstPage = false`
+4. A draft script.. Still need update.