add live preview (hot-reloading) for docs using sphinx-autobuild

[kskarthik]

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• The pull request should include overview of the suggested solution
• If the pull requests changes current behavior, reasons why your solution is better.
• The proposed code should be fully functional
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• The proposed tests should ensure significative code coverage
• All new and existing tests should pass

[kskarthik]

the reason for this patch is that, It was easy to edit the docs with live preview option. We could visualize our changes locally. So, i have implemented it.