Issue 8: Add issue templates

[tisonkun]

Visual results with this patch

You can also try it out by creating issues in https://github.com/TisonKun/TubeMQ (issues -> New Issue)

[tisonkun]

@gosonzhang @yiheng @guangxuCheng Could you take a look?

[guangxuCheng]

lgtm

[tisonkun]

Thanks for your review @guangxuCheng! I don't have write access to the repo so it would be helpful if you help to merge it.

Besides, I am not sure whether the format "Issue 8: ..." is ok. But before a standard output from #15 all readable format should be valid.

[yiheng]

This looks great. Only one concern, have we decided to use github issues to manage our tickets?

[tisonkun]

@yiheng At least RocketMQ adopts GitHub issue as issue tracker so I think it wouldn't be a blocker that we use GitHub issue as issue tracker.

I agree that it is an open issue which issue tracker we finally adopt. But it wouldn't block this pull request that we make current state a bit better.