Add issue template

[gegoune]

To minimise number of round trips between reporters and maintainers we should introduce issue template to this repository.

I think very good example, which we should use in my opinion, is one from Lewis' gitsigns plugin.

[alex-courtis]

Absolutely... I've been asking a lot lately...

That looks nice and small.

[gegoune]

Also avoids packer, which is not maintained any more.

[alex-courtis]

Oh damn... I liked packer...

Not going to go with lazy though ;)

[alex-courtis]

The approach of "git clone, no plugin manager" is probably best for nvim-tree too.

[gegoune]

Yes, it is. I would like to add the same template to nvim-tree too.

There is pckr.nvim that I happily use. Very similar experience to packer. pckr started as a refactor of packer.

[alex-courtis]

Oh nice, lewis... a respected member of the community.

I'll give it a go.