Only greeting the new contributors

[atinba]

I think we should greet new contributors only since after a few contribution we get the idea about the contribution guidelines and also the greeting message in each issue and PR also clutters them a bit.

We can use the welcome bot for this, we only need to specify the greeting messages

[TawfikYasser]

@atin Hi,
This is a good idea

If you can do that raise a PR

[ming-tsai]

May be for first time contributor

[atinba]

@ming-tsai we have to install the welcome bot in this repo, i think only you can do that, i've sent you a request for that.

[atinba]

@ming-tsai Have you accepted the request? You can also add it your self from here