add issue template

[vincentsarago]

Let's make it clear what user should write to avoid issues like #546 #545

ref: https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests

Here is a simple template we have at devseed

<!-- Please search existing issues to avoid creating duplicates. -->


#### Problem description

[this should explain **why** the current behavior is a problem and why the expected output is a better solution.]

#### Expected Output


#### Environment Information

Os, Python version, ...