Integrate npm package "doctoc" to update README.md

README.md

@@ -14,6 +14,8 @@ Still in the early stage, feel free to fork or contribute to HackMD.
 
 Thanks for using! :smile:
 
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 # Table of Contents
 
 - [Browsers Requirement](#browsers-requirement)
@@ -35,6 +37,8 @@ Thanks for using! :smile:
   - [Operational Transformation](#operational-transformation)
 - [License](#license)
 
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+
 # Browsers Requirement
 
 - Chrome >= 47, Chrome for Android >= 47